The phase 2 trial and the FDA notice: ipamorelin side effects on record

Ipamorelin side effects are the question this article is built around. The recorded evidence is thin: the one controlled human trial (a phase 2 study of 117 patients after bowel surgery) showed no significant difference from placebo and recorded treatment-emergent adverse events in 87.5 per cent of the ipamorelin group and 94.8 per cent of the placebo group, animal studies recorded more fat-pad weight in mice, and the FDA lists ipamorelin acetate in category 2 for compounding, a category for substances that may present significant safety risks. It sets out what the published papers and the US Food and Drug Administration recorded, including the one human efficacy trial, which did not show a significant benefit, and what nobody yet knows. It also explains what ipamorelin is: a synthetic peptide made of five amino acids, described in 1998 as a growth hormone secretagogue. Listings (laboratory research only, 18+): ipamorelin capsules.

Key takeaways

• Ipamorelin is a pentapeptide described in 1998 as a growth hormone secretagogue, meaning a compound that prompts growth hormone (GH) release by acting on a GHRP-like receptor (Raun et al., 1998), now generally described as the ghrelin receptor (Venkova et al., 2009).
• In the discovery paper, ipamorelin released GH in rat pituitary cells, anaesthetised rats and conscious swine, and in swine did not raise ACTH or cortisol significantly beyond the level seen with GHRH. These were preclinical experiments with no human data.
• Only one registered human efficacy trial was found: a phase 2 study of intravenous ipamorelin after bowel surgery in 117 patients, which showed no statistically significant difference from placebo on its key endpoint (Beck et al., 2014).
• The other human pharmacology data are a 1999 study in healthy men given short intravenous infusions (Gobburu et al., 1999), plus a 2015 doping-control study in which one volunteer was given ipamorelin nasally (Semenistaya et al., 2015).
• No human study of oral ipamorelin was found, so nothing from injection, intravenous or animal work can be assumed to apply to a capsule.
• Recent reviews call the growth hormone secretagogue peptides investigational, with uncertain safety and product-quality concerns; the World Anti-Doping Agency (WADA) lists ipamorelin as prohibited.
• The side-effects section collects the adverse or safety-relevant findings from the sources reviewed, and the comparison section sets ipamorelin beside MK-677 and somatropin (HGH) without ranking them; no head-to-head human trial was found.
• Research compounds sold by Free Muscle are supplied for laboratory research use only and are not for human consumption. They are not authorised as medicines by the MHRA, EMA or FDA, are not food supplements, and are sold only to adults aged 18 or over. Nothing on this page is medical or dosing advice.

What is ipamorelin?

Ipamorelin is a laboratory-made peptide. A peptide is simply a short chain of amino acids, the building blocks of proteins. Ipamorelin has five, written as Aib-His-D-2-Nal-D-Phe-Lys-NH2, and several of those units are not found in natural proteins. That is one reason the molecule is relatively hard to characterise, a point the US Food and Drug Administration (FDA) also makes on its compounding page, which we cover below.

The authors of the original paper arrived at it through a major chemistry programme. According to Raun et al. (1998), ipamorelin came from a series of compounds built by removing the central two-amino-acid segment of an older peptide called growth hormone-releasing peptide-1 (GHRP-1). The same paper described it as the first compound of its type with a selectivity for GH release similar to that of growth hormone-releasing hormone (GHRH), the body's own signal.

Two related terms are worth defining. A secretagogue is a substance that makes a gland secrete something; here, the pituitary gland secreting GH. A ghrelin mimetic is a compound that imitates ghrelin, a hormone made in the stomach that stimulates appetite and gut movement (Venkova et al., 2009; Ahnfelt-Rønne et al., 2001). Ipamorelin is described in the literature as both. A 2016 review of ghrelin receptor drugs concluded that, apart from one compound approved for diagnostic use in Japan, none of the candidates has been successfully introduced to the market (Vodnik et al., 2016). That review is now ten years old and is not a live register check; it describes the wider family of ghrelin-receptor ligands to which ipamorelin belongs (Venkova et al., 2009).

In short: ipamorelin is a research peptide that has been studied in cells, animals and a small number of human trials, and that has not become an approved medicine in the sources reviewed here.

How researchers think it works

Growth hormone release from the pituitary is regulated by growth hormone-releasing hormone (GHRH) and somatostatin, and growth hormone secretagogues can also act on GH secretion (Jiménez-Reina et al., 2002). The ghrelin receptor is also called GHS-R1a (Vodnik et al., 2016). In the discovery paper, experiments using GHRP and GHRH antagonists showed that ipamorelin, like GHRP-6, stimulated GH release via a GHRP-like receptor (Raun et al., 1998).

Because ghrelin-receptor stimulation has been reported to have promotility effects in the gut (Beck et al., 2014), researchers asked whether ipamorelin might influence digestion. In an isolated-tissue experiment using rat stomach, gastric muscle contractions that had been suppressed by surgery were reversed by ipamorelin and by ghrelin, which the authors linked to a ghrelin receptor mechanism involving cholinergic nerves (Greenwood-Van Meerveld et al., 2012). Beck and colleagues reported a trial of ipamorelin in post-operative ileus in 2014, described below.

Key studies at a glance

The evidence, study by study

There are only two published human efficacy or pharmacokinetic studies of ipamorelin in the sources reviewed for this article: a 1999 healthy-volunteer pharmacokinetic study and a 2014 phase 2 trial in surgical patients (plus a one-volunteer nasal urine-testing study discussed under doping laboratories). No human study of body composition, muscle, fat loss, sleep or recovery was found. Everything else below comes from cells, animals or analytical chemistry. Each summary reports what happened in that study population only.

Raun et al., 1998: the discovery and selectivity paper

This European Journal of Endocrinology paper reported the pharmacology of the new peptide in three systems. In primary rat pituitary cells, ipamorelin released GH with a half-maximal effective concentration of 1.3 nanomoles per litre and a maximum effect of 85 per cent, against 2.2 nanomoles per litre and 100 per cent for GHRP-6. Potency and efficacy were described as comparable to GHRP-6 in anaesthetised rats and very similar in conscious swine. The dose levels are given in the paper (Raun et al., 1998).

The selectivity result is the paper's headline claim. In swine, none of the secretagogues tested changed plasma FSH, LH, prolactin or TSH. GHRP-6 and GHRP-2 raised ACTH and cortisol. Ipamorelin did not raise them to levels significantly different from those after GHRH, even at doses more than 200-fold higher than needed for GH release. The authors concluded that ipamorelin was the first GHRP-receptor agonist with GH selectivity similar to GHRH.

Limitations: this was a pharmacology paper in cells, rats and pigs. The abstract reports no human data and no long-term or toxicology findings.

Gobburu et al., 1999: healthy volunteers, intravenous infusion

This was a dose-escalation trial with five intravenous infusion rates, given as short infusions to eight healthy men per level. Blood levels of the peptide were dose-proportional, with a terminal half-life of 2 hours, a clearance of 0.078 litres per hour per kilogram and a steady-state volume of distribution of 0.22 litres per kilogram. GH rose in a single episode peaking at 0.67 hours and falling to negligible levels at every level. Variation between individuals was larger for the hormone response than for the blood levels of the peptide (Gobburu et al., 1999).

Limitations: the abstract reports no adverse-event findings, the participants were healthy men only, the infusions were intravenous and brief, and the study was designed to describe pharmacokinetics, not to test any clinical benefit.

Beck et al., 2014: the post-operative ileus trial (NCT00672074)

Post-operative ileus is a temporary slowing or stalling of the gut after abdominal surgery. Because ghrelin-receptor stimulation has been reported to have promotility effects in the gut, a phase 2 trial tested ipamorelin in this setting. It was multicentre, double-blind and placebo-controlled. It enrolled 117 adults having small or large bowel resection, by open or laparoscopic surgery, and 114 formed the safety and modified intention-to-treat populations. Patients received intravenous ipamorelin or placebo during their hospital stay; the dose and schedule are given in the paper (Beck et al., 2014).

The key efficacy endpoint was the time from the first study dose to tolerating a standardised solid meal. The median was 25.3 hours with ipamorelin and 32.6 hours with placebo, a difference that was not statistically significant (p = 0.15). Any treatment-emergent adverse event occurred in 87.5 per cent of the ipamorelin group and 94.8 per cent of the placebo group. The authors described the drug as well tolerated and reported no significant differences from placebo in the key or secondary efficacy analyses.

Limitations, as stated by the authors: the proof-of-concept study was small and enrolled patients with a broad range of underlying conditions. The trial registry shows it was sponsored by Helsinn Therapeutics (U.S.), Inc., with a completion date of December 2009. A trial that was completed without a significant benefit is not evidence that the compound works, and it says nothing about use outside a hospital or by another route.

Venkova et al., 2009, and Greenwood-Van Meerveld et al., 2012: rat models of post-operative ileus

Rodent studies in the same model were also published. In fasted male rats subjected to laparotomy and bowel manipulation, a single intravenous bolus of ipamorelin shortened the time to the first bowel movement but did not change cumulative droppings, food intake or weight gain at 48 hours. Repeated dosing (the schedule is in the paper) did significantly increase droppings, food intake and weight gain (Venkova et al., 2009). The protocol doses are in the paper.

A second paper reported gastric emptying in a similar surgical model. After surgery, 78 per cent (plus or minus 5) of a test meal stayed in the stomach in vehicle-treated rats. With intravenous ipamorelin, 52 per cent (plus or minus 11) remained, compared with 44 per cent (plus or minus 6) in rats that had not had surgery. In isolated stomach tissue, surgery-suppressed contractions were reversed by ipamorelin and ghrelin (Greenwood-Van Meerveld et al., 2012).

Limitations: both in vivo studies used male rats and intravenous administration, and both are models. The human trial did not reproduce a significant benefit on its main endpoint, which illustrates why animal results cannot be assumed to carry over to patients.

Johansen et al., 1998: how the peptide is handled in rats, and the nasal route

In male rats, ipamorelin had a plasma clearance five-fold lower than GHRP-6 after intravenous injection and was excreted mainly in urine, whereas GHRP-6 was excreted mainly in bile. After intranasal application, bioavailability was estimated at roughly 20 per cent, lower than the roughly 50 per cent estimated for three of the other peptides (Johansen et al., 1998). The abstract reports intravenous and intranasal routes only and gives no oral data.

Hansen et al., 1998: designing oral compounds from ipamorelin

A 1998 medicinal chemistry paper used ipamorelin as the lead compound for smaller molecules with a lower hydrogen-bonding potential, aiming for oral bioavailability. Most of the compounds tested had oral bioavailability of 10 to 55 per cent in dogs (Hansen et al., 1998). The abstract does not report oral bioavailability for ipamorelin itself. A separate 2001 paper described NN703, an orally active compound derived from GHRP-1 via ipamorelin, as having entered phase II clinical trials (Ahnfelt-Rønne et al., 2001); the abstract does not report any trial results.

Bone, body weight and body fat in rodents

Several rodent studies looked at growth and body composition, and the results include findings that cut both ways.

• In a 15-day study in adult female rats, ipamorelin increased the rate of longitudinal bone growth dose-dependently, from 42 micrometres a day in the vehicle group to 44, 50 and 52 micrometres a day, with a dose-dependent rise in body weight. Total IGF-I and bone turnover markers were unchanged, and the GH response to a repeat challenge was marginally reduced (Johansen et al., 1999).
• In a 12-week study in 13-week-old female rats, body weight and total bone mineral content measured by DXA rose, but bone mineral content corrected for body weight and volumetric bone density did not change. The authors attributed the increases to larger bones, not denser ones (Svensson et al., 2000).
• In mice, ipamorelin produced a small 15 per cent body weight increase by two weeks and raised fat pad weight relative to body weight. In GH-intact mice, two weeks of ipamorelin or GHRP-6 raised relative body fat on DEXA, and the secretagogues, unlike GH, raised serum leptin and food intake. The authors concluded that these compounds increase body fat by GH-independent mechanisms that may include increased feeding (Lall et al., 2001).
• In a 21-day study in young female rats, the ultrastructure of pituitary somatotroph cells was unchanged, but the volume density of secretion granules increased, and basal intracellular GH content in cultured somatotrophs was lower than in saline-treated animals (Jiménez-Reina et al., 2002).

Taken together, these papers show that in rodents, increases in body weight and in the rate of longitudinal bone growth were accompanied by increased fat mass and food intake in mice, by increases in bone mineral content that the authors attributed to larger bones rather than denser bone in rats, and by a slightly blunted pituitary response to a repeat challenge. None of them involved people or oral dosing.

Safety signals and what regulators and doping laboratories say

Trial adverse events. In the only controlled human efficacy trial, adverse events were common in both arms in patients who had just had major surgery, and the authors judged the drug well tolerated over the study period (Beck et al., 2014). Treatment was confined to the post-operative hospital stay (the schedule is given in the paper), and the sources reviewed report no controlled-trial data on long-term exposure. A 2026 critical review described the long-term risks of peptides in sport as poorly defined (Coutinho et al., 2026).

FDA. The FDA lists ipamorelin acetate in category 2 of its list of drug substances for compounding, described as substances that may present significant safety risks, with the entry dated 29 September 2023. The agency's page, current as of 22 April 2026, says compounded products containing it may carry a risk of immunogenicity for certain routes because of potential aggregation or peptide-related impurities, and notes that it contains unnatural amino acids that complicate characterisation. It also states that a published study identified serious adverse events, including death, when ipamorelin was given intravenously to improve gastric motility, and that it has not identified safety information for certain other injectable routes (FDA compounding page). That is the FDA's wording; the abstract of the Beck trial does not mention deaths, and the study the FDA refers to is not identified here.

Recent reviews. A 2026 review of performance-enhancing peptides that act on the GH-IGF-1 axis, including ipamorelin, lists reported adverse effects across endocrine and metabolic disturbances (prolactin and cortisol elevations, appetite changes and dysglycaemia), fluid retention, muscle and joint pain, and injection-site reactions, and stresses uncertainty about product composition and dose in unregulated supply chains (Dominikowski et al., 2026). The abstract lists these effects for the group of agents reviewed and does not attribute them to ipamorelin specifically. A structured review concluded that growth hormone secretagogues such as ipamorelin remain investigational, with uncertain safety profiles, product quality concerns and widespread anti-doping restrictions (Villegas Meza et al., 2026). A sports-medicine narrative review found that rigorous human safety data are scarce for the unapproved peptides it covered, a list that includes ipamorelin (Mendias and Awan, 2026), and a critical review of peptide use in sport described the clinical evidence as limited and the supply chain as one where products are often mislabelled or contaminated (Coutinho et al., 2026).

Doping laboratories. Analytical chemists have developed urine tests for these peptides. One group gave ipamorelin nasally to a single volunteer and found it was metabolised extensively, with a breakdown product still detectable after the parent compound had gone, and noted that the detection window depends on individual metabolism, preparation and route (Semenistaya et al., 2015). A 2011 mass-spectrometry method covered ipamorelin and other peptides in urine, with a detection limit of 0.2 to 1 nanogram per millilitre (Thomas et al., 2011). That paper described the peptide class as orally active, but its proof-of-principle used an oral dose of a different compound, GHRP-2, so it does not show that ipamorelin is absorbed by mouth. An analysis of black-market products identified Gly-Ipamorelin, ipamorelin with an extra glycine at one end, confirmed by custom synthesis, as evidence that unregulated products can contain modified analogues (Krug et al., 2018).

What the research does not tell us

The evidence hierarchy is thin. Evidence ranges from cell experiments at the bottom, through animal studies and small human pharmacology studies, to randomised trials, systematic reviews and regulatory approval. In the sources reviewed, the human efficacy record is a single phase 2 trial with no significant difference from placebo on its key endpoint. No systematic review or meta-analysis of the compound was found. Anecdotal reports, whether in forums or on social media, are not evidence of safety or effect, and one review discussed the placebo effect and how social media amplifies it (Mendias and Awan, 2026).

Route and formulation matter. Every human efficacy or pharmacokinetic study found used intravenous infusion; the only other human data are an analytical study in which one volunteer was given a nasal dose (Semenistaya et al., 2015). Animal work used subcutaneous, intravenous and intranasal routes, plus cell cultures and a minipump in one long study. No published study of oral ipamorelin, in capsules or any other form, was found, and no oral bioavailability data for ipamorelin itself exist in the sources reviewed. The medicinal chemistry paper above redesigned the molecule to obtain oral compounds, and the Free Muscle listing itself notes that peptides taken by mouth are largely broken down by digestive enzymes. For a wider discussion, see our explainer on whether oral peptides work. The practical consequence is that nothing in the injection, intravenous or animal literature can be assumed to apply to a capsule.

Specific gaps.

• The longest human treatment period found was the hospital stay in the Beck trial; long-term human safety data were not found in the sources reviewed.
• No source reviewed reports long-term human data on glucose regulation, prolactin, cortisol or body fat; the Free Muscle product page states that effects on glucose regulation and long-term safety are not established.
• No human trial of muscle, fat loss, sleep, recovery or anti-ageing outcomes was found in the sources reviewed.
• No source in this set reports independent testing of the identity or purity of any particular product sold in unregulated supply (the FDA page raises peptide-related impurities as a concern for compounded ipamorelin); the only information on batch testing for the listing discussed below is the seller's own statement.

Ipamorelin results: what the studies actually measured

Anyone searching for ipamorelin results will find no single headline figure: outcomes differ by population and design, and in the one human efficacy trial found, the difference from placebo on the key endpoint was not statistically significant (Beck et al., 2014). The outcomes below are grouped by type, each with its study, and describe only that study population. The figures repeat those in the study-by-study section, except the ferret result (Lu et al., 2024), which is reported only here, and they are regrouped so that each sits beside its limits.

Growth hormone release. The consistent outcome in the pharmacology papers was a rise in GH. In cultured rat pituitary cells, ipamorelin reached a maximum effect of 85 per cent, against 100 per cent for GHRP-6 (Raun et al., 1998). In eight healthy men per level, given brief intravenous infusions, GH rose in a single episode that peaked at 0.67 hours, and the peptide's terminal half-life was 2 hours (Gobburu et al., 1999).

Gut function in the one human efficacy trial. In the phase 2 trial (double-blind, placebo-controlled, intravenous, in adults having bowel resection), the median time to the first tolerated standardised meal was 25.3 hours with ipamorelin and 32.6 hours with placebo, a difference that was not significant (p = 0.15) (Beck et al., 2014).

Gut function and weight in animal models. In male rats after abdominal surgery, 52 per cent of a test meal remained in the stomach after intravenous ipamorelin, against 78 per cent in vehicle-treated rats and 44 per cent in rats that had not had surgery (Greenwood-Van Meerveld et al., 2012). In ferrets given cisplatin, intraperitoneal ipamorelin did not change vomiting, but weight loss on the last day of the delayed phase was inhibited by approximately 24 per cent (Lu et al., 2024).

Growth and body composition in animals. In a 15-day injection study in adult female rats, longitudinal bone growth rose from 42 to 52 micrometres a day at the top level (Johansen et al., 1999). In a 12-week study in young adult female rats, total bone mineral content rose, but it did not rise once corrected for body weight, which the authors attributed to larger bones rather than denser ones (Svensson et al., 2000). In GH-intact mice, two weeks of ipamorelin or GHRP-6 raised relative body fat on DEXA, and the secretagogue treatment (unlike GH) also raised serum leptin and food intake; ipamorelin raised fat-pad weight relative to body weight in both GH-deficient and GH-intact mice (Lall et al., 2001).

Limits and adverse findings in the same literature. No human study of body composition, muscle, fat loss, sleep or recovery was found. The human trial recorded treatment-emergent adverse events in 87.5 per cent of the ipamorelin group and 94.8 per cent of the placebo group, and the mice recorded more fat-pad weight, and GH-intact mice more body fat, leptin and food intake (see the side-effects section). Most evidence comes from cell culture, animals and intravenous use; no oral capsule study was found, so none of these results can be assumed to apply to one. A 2026 structured review calls growth hormone secretagogues, including ipamorelin, investigational (Villegas Meza et al., 2026).

Ipamorelin side effects reported in the research

The table collects the adverse or safety-relevant findings from the sources reviewed. Findings from cells and rodents describe those animals, and class-level review statements are not attributed to ipamorelin specifically.

What case reports can and cannot show. No case report of an adverse event attributed to ipamorelin was found in the sources reviewed. For the neighbouring compound MK-677, a 2025 case report described raised liver enzymes in one otherwise healthy man who had taken it as a supplement, with liver tests returning to normal after he stopped (Cobani et al., 2025). A report of that kind shows an event occurred alongside exposure to a product. It cannot show how often it happens, whether the compound rather than something else in the product caused it, or what the product contained; an analytical study found modified analogues, including Gly-Ipamorelin, in black-market products (Krug et al., 2018), and a 2026 critical review described products in the unregulated supply chain as often mislabelled or contaminated (Coutinho et al., 2026).

Data gaps. The controlled human record is one phase 2 trial confined to a hospital stay, with no long-term or oral data and no systematic review. Reviews list adverse effects for groups of peptides, and one found rigorous human safety data scarce (Mendias and Awan, 2026). Anecdotal reports are not evidence and are not used here.

Ipamorelin vs MK-677 vs HGH (somatropin): how they differ

The three names are sometimes compared, but they are different kinds of substance. The table compares them on points the sources evidence and does not rank them; no head-to-head human trial was found in the sources reviewed.

The differences are of kind rather than degree. Ipamorelin (Raun et al., 1998; Venkova et al., 2009) and MK-677 (Liu et al., 2021) both act on the ghrelin receptor, while somatropin is the hormone itself. Two rodent papers in the sources included a GH arm alongside ipamorelin: in mice the two differed in their effects on body fat, leptin and food intake (Lall et al., 2001), and in adult female rats GH and the secretagogues all raised body weight and total bone mineral content (Svensson et al., 2000). No human comparison was found. Evidence for one compound is not evidence for another, and most ipamorelin evidence concerns cells, animals and intravenous use, so it cannot be assumed to apply to an oral capsule. For the trials in full, see our MK-677 clinical trials article. This is general information, not legal advice.

Legal and anti-doping status in brief

This is general information, not legal advice.

Anti-doping. According to the WADA Prohibited List page (fetched 2 October 2026), ipamorelin is named under section S2, peptide hormones, growth factors, related substances and mimetics, in sub-class S2.2.4 on growth hormone releasing factors, with other secretagogues. The class is prohibited at all times and its substances are non-specified substances. The List is updated at least annually and comes into force on 1 January. See the WADA Prohibited List. Athletes should check the current position with their governing body.

UK medicines law. Under regulation 2 of the Human Medicines Regulations 2012, a medicinal product includes any substance that may be administered to people with a view to restoring, correcting or modifying a physiological function by a pharmacological, immunological or metabolic action, or to make a medical diagnosis (regulation 2). Regulation 46 says a person may not sell or supply an unauthorised medicinal product (regulation 46). Whether a given product is a medicinal product is for the Medicines and Healthcare products Regulatory Agency (MHRA) and the courts to decide. According to the MHRA's borderline products guidance, last updated 2 July 2026, the agency looks at the claims made, the intended purpose and how a product is presented.

The MHRA guidance page linked above does not mention ipamorelin, and this article does not say whether the MHRA or a court has classified it. People with a concrete question should take qualified advice.

Full breakdown with sources: Is ipamorelin legal in the UK?

About the Free Muscle ipamorelin listings

Free Muscle sells research compounds and gym apparel online at freemuscle.co.uk. The listing relevant to this article is Ipamorelin, 60 capsules; the strength per capsule is not stated on the product page. The page states that the product is not authorised as a medicine or food supplement in the UK or EU, that growth hormone secretagogues are on the WADA Prohibited List, that development of the compound was discontinued after early clinical work, and that the capsule form is not claimed to match injection. It also says effects on glucose regulation and long-term safety have not been established. Readers who want the full list of peptide research products can browse the peptides collection.

Research compounds sold by Free Muscle are supplied for laboratory research use only and are not for human consumption. They are not authorised as medicines by the MHRA, EMA or FDA, are not food supplements, and are sold only to adults aged 18 or over. Nothing on this page is medical or dosing advice.

• Batch testing. Every batch of research compounds is assayed for identity and purity by Janoshik Analytical, an independent laboratory. The Certificate of Analysis for a batch is sent on request: email the batch number printed on the label together with the product name. Details are on the lab tests page, and our guide explains how to read a certificate of analysis.

Frequently asked questions

What is ipamorelin in simple terms?

A synthetic five-amino-acid peptide that prompted GH release in cells and animals in 1998 (Raun et al., 1998).

Is ipamorelin the same thing as growth hormone?

No. Growth hormone is a large protein (Krug et al., 2018). Ipamorelin is a small peptide that, in the studies described above, prompted the pituitary to release the body's own GH. A mouse study found that the secretagogues and GH itself differed in their effects on body fat, leptin and food intake (Lall et al., 2001).

Did the human clinical trial of ipamorelin succeed?

Not on its key endpoint. In the phase 2 post-operative ileus trial, the difference in time to the first tolerated meal between ipamorelin and placebo was not statistically significant (Beck et al., 2014).

Is there any research on ipamorelin capsules?

None was found. The human efficacy and pharmacokinetic studies used intravenous infusion, one analytical study gave a single volunteer a nasal dose, and the animal studies used other routes. The nearest oral work was a 1998 medicinal-chemistry programme that used ipamorelin as a lead compound for redesigned molecules tested in dogs (Hansen et al., 1998). Results from one route cannot be assumed for another.

How did ipamorelin differ from GHRP-6 and GHRP-2 in the discovery paper?

In swine, GHRP-6 and GHRP-2 raised ACTH and cortisol, while ipamorelin did not raise them significantly beyond GHRH (Raun et al., 1998), a preclinical observation. A 2026 review lists prolactin and cortisol elevations among the adverse effects reported for the wider group of GH-axis peptides it covered, without attributing them to ipamorelin specifically (Dominikowski et al., 2026).

Is ipamorelin on the WADA Prohibited List?

Yes. The WADA List names it under S2.2.4 among growth hormone secretagogues, and the class is prohibited at all times (WADA Prohibited List).

What is the legal position of ipamorelin in the UK?

The MHRA guidance page does not mention ipamorelin. UK law sets out a general definition of a medicinal product and a general rule against selling unauthorised ones, and the MHRA applies its published test to borderline products. Our companion article on ipamorelin UK legal status and quality checks goes into the position in more detail. This is general information, not legal advice.

Why do batch certificates matter for peptides?

A 2026 critical review described products in the largely unregulated supply chain as often mislabelled or contaminated (Coutinho et al., 2026), and an analytical study identified modified analogues, including Gly-Ipamorelin, in black-market products (Krug et al., 2018). An independent assay result for a batch addresses identity and purity of that batch only, and our lab tests page explains how Free Muscle handles requests for certificates.

What ipamorelin side effects have been reported in research?

The one controlled human trial recorded treatment-emergent adverse events in 87.5 per cent of the ipamorelin group and 94.8 per cent of the placebo group after bowel surgery (Beck et al., 2014). Animal studies recorded more fat-pad weight in mice, and more body fat and food intake in GH-intact mice (Lall et al., 2001) and a marginally reduced GH response to a repeat challenge in rats (Johansen et al., 1999), and the FDA raises immunogenicity and impurity concerns for compounded products (FDA compounding page). The side-effects section sets out the findings.

What does ipamorelin do, and what results have studies reported?

In rat pituitary cells, rats and swine it prompted GH release via a GHRP-like receptor (Raun et al., 1998), and in healthy men given brief intravenous infusions GH rose in a single episode (Gobburu et al., 1999). The one human efficacy trial found no significant difference from placebo on its key endpoint (Beck et al., 2014). The results section groups the measured outcomes with their limits.

How does ipamorelin differ from MK-677 and from HGH (somatropin)?

Ipamorelin is a five-amino-acid peptide acting on a GHRP-like receptor now described as the ghrelin receptor (Raun et al., 1998; Venkova et al., 2009), and MK-677 is a non-peptide molecule that also acts on the ghrelin receptor (Liu et al., 2021), whereas somatropin is growth hormone itself (Krug et al., 2018). Their evidence bases and legal positions also differ, and no head-to-head human trial was found. See the comparison section, our MK-677 clinical trials article and our article on whether HGH is legal in the UK.

What is the half-life of ipamorelin?

In eight healthy men per level given brief intravenous infusions, the terminal half-life was 2 hours (Gobburu et al., 1999). That is an intravenous result in volunteers; the abstract gives nothing for other routes, and it cannot be assumed for a capsule.

Does this article give instructions or doses for ipamorelin?

No. This article publishes no dose or protocol; the protocols used in each study are in the linked papers, for example Beck et al., 2014 and Johansen et al., 1999. Free Muscle sells ipamorelin for laboratory research use only, to customers aged 18 or over; it is not a medicine or food supplement and not for human consumption. Nothing here is medical advice.

How do anti-doping laboratories detect ipamorelin?

Analytical chemists have published urine methods for it. In one nasal study, ipamorelin was given to a single volunteer and a metabolite was detected after the parent compound had gone (Semenistaya et al., 2015), and a 2011 method had a detection limit of 0.2 to 1 nanogram per millilitre for a group of peptides that included it (Thomas et al., 2011). The WADA Prohibited List lists ipamorelin as prohibited.

Related reading

• Short overview: Ipamorelin research guide: trials, side effects and UK status

Sources

1. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-61. doi:10.1530/eje.0.1390552. PMID 9849822
2. Gobburu JV, Agersø H, Jusko WJ, Ynddal L. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res. 1999;16(9):1412-6. doi:10.1023/a:1018955126402. PMID 10496658
3. Beck DE, Sweeney WB, McCarter MD, Ipamorelin 201 Study Group. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. Int J Colorectal Dis. 2014;29(12):1527-34. doi:10.1007/s00384-014-2030-8. PMID 25331030
4. Venkova K, Mann W, Nelson R, Greenwood-Van Meerveld B. Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus. J Pharmacol Exp Ther. 2009;329(3):1110-6. doi:10.1124/jpet.108.149211. PMID 19289567
5. Greenwood-Van Meerveld B, Tyler K, Mohammadi E, Pietra C. Efficacy of ipamorelin, a ghrelin mimetic, on gastric dysmotility in a rodent model of postoperative ileus. J Exp Pharmacol. 2012;4:149-55. doi:10.2147/JEP.S35396. PMID 27186127
6. Johansen PB, Hansen KT, Andersen JV, Johansen NL. Pharmacokinetic evaluation of ipamorelin and other peptidyl growth hormone secretagogues with emphasis on nasal absorption. Xenobiotica. 1998;28(11):1083-92. doi:10.1080/004982598238976. PMID 9879640
7. Hansen TK, Ankersen M, Hansen BS, et al. Novel orally active growth hormone secretagogues. J Med Chem. 1998;41(19):3705-14. doi:10.1021/jm980197u. PMID 9733496
8. Ahnfelt-Rønne I, Nowak J, Olsen UB. Do growth hormone-releasing peptides act as ghrelin secretagogues? Endocrine. 2001;14(1):133-5. doi:10.1385/ENDO:14:1:133. PMID 11322495
9. Johansen PB, Nowak J, Skjaerbaek C, et al. Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats. Growth Horm IGF Res. 1999;9(2):106-13. doi:10.1054/ghir.1999.9998. PMID 10373343
10. Svensson J, Lall S, Dickson SL, et al. The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats. J Endocrinol. 2000;165(3):569-77. doi:10.1677/joe.0.1650569. PMID 10828840
11. Lall S, Tung LY, Ohlsson C, Jansson JO, Dickson SL. Growth hormone (GH)-independent stimulation of adiposity by GH secretagogues. Biochem Biophys Res Commun. 2001;280(1):132-8. doi:10.1006/bbrc.2000.4065. PMID 11162489
12. Jiménez-Reina L, Cañete R, de la Torre MJ, Bernal G. Influence of chronic treatment with the growth hormone secretagogue ipamorelin, in young female rats: somatotroph response in vitro. Histol Histopathol. 2002;17(3):707-14. doi:10.14670/HH-17.707. PMID 12168778
13. Semenistaya E, Zvereva I, Thomas A, et al. Determination of growth hormone releasing peptides metabolites in human urine after nasal administration of GHRP-1, GHRP-2, GHRP-6, hexarelin, and ipamorelin. Drug Test Anal. 2015;7(10):919-25. doi:10.1002/dta.1787. PMID 25869809
14. Thomas A, Höppner S, Geyer H, et al. Determination of growth hormone releasing peptides (GHRP) and their major metabolites in human urine for doping controls by means of liquid chromatography mass spectrometry. Anal Bioanal Chem. 2011;401(2):507-16. doi:10.1007/s00216-011-4702-3. PMID 21298258
15. Krug O, Thomas A, Malerød-Fjeld H, et al. Analysis of new growth promoting black market products. Growth Horm IGF Res. 2018;41:1-6. doi:10.1016/j.ghir.2018.05.001. PMID 29864719
16. Mendias CL, Awan TM. Safety and efficacy of approved and unapproved peptide therapies for musculoskeletal injuries and athletic performance. Sports Med. 2026;56(8):1921-1935. doi:10.1007/s40279-026-02437-0. PMID 41966639
17. Dominikowski A, Rękoś Z, Olejarz M, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. doi:10.3389/fendo.2026.1822475. PMID 42395176
18. Villegas Meza AD, Nocek M, Mitchell BC, et al. Injectable peptides in sports medicine: a structured narrative review of evidence, safety, and antidoping implications. JBJS Rev. 2026;14(5). doi:10.2106/JBJS.RVW.26.00027. PMID 42160466
19. Coutinho LFD, De Oliveira Neves LF, Camilo RP. A new era of doping? Use of peptide and peptide-analog drugs in recreational and professional sport and bodybuilding: a critical review. J Sports Med Phys Fitness. 2026;66(7):880-885. doi:10.23736/S0022-4707.26.17773-1. PMID 41880199
20. Vodnik M, Štrukelj B, Lunder M. Ghrelin receptor ligands reaching clinical trials: from peptides to peptidomimetics; from agonists to antagonists. Horm Metab Res. 2016;48(1):1-15. doi:10.1055/s-0035-1564149. PMID 26551992
21. Lu Z, Ngan MP, Liu JYH, et al. The growth hormone secretagogue receptor 1a agonists, anamorelin and ipamorelin, inhibit cisplatin-induced weight loss in ferrets: Anamorelin also exhibits anti-emetic effects via a central mechanism. Physiol Behav. 2024;284:114644. doi:10.1016/j.physbeh.2024.114644. PMID 39043357
22. Svensson J, Lönn L, Jansson JO, et al. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab. 1998;83(2):362-9. doi:10.1210/jcem.83.2.4539. PMID 9467542
23. Nass R, Pezzoli SS, Oliveri MC, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-11. doi:10.7326/0003-4819-149-9-200811040-00003. PMID 18981485
24. Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Sex Med Rev. 2018;6(1):45-53. doi:10.1016/j.sxmr.2017.02.004. PMID 28400207
25. Liu H, Sun D, Myasnikov A, et al. Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren. Nat Commun. 2021;12(1):6410. doi:10.1038/s41467-021-26735-5. PMID 34737341
26. Cobani E, Amin MS, Hasso M, Kumbar L. Hepatotoxicity induced by MK-677. BMJ Case Rep. 2025;18(7). doi:10.1136/bcr-2025-265728. PMID 40675653
27. World Anti-Doping Agency. Prohibited List (accessed 2 October 2026).
28. US Food and Drug Administration. Certain drug substances for use in compounding that may present significant safety risks (content current as of 22 April 2026).
29. Human Medicines Regulations 2012, regulation 2 and regulation 46. legislation.gov.uk.
30. MHRA. Borderline products: how to tell if your product is a medicine (last updated 2 July 2026). gov.uk.