Ipamorelin research guide: trials, side effects and UK status

Most searches for ipamorelin ask one of four things: what the peptide is and why it is called selective, whether it has been tested in people and with what result, whether it is legal to buy in the UK, and how it relates to CJC-1295, tesamorelin, sermorelin and MK-677. This guide answers each from the published record, including the parts that do not flatter the compound. Free Muscle sells it for laboratory research only, to adults, and nothing here is guidance on using it.

What is ipamorelin?

Ipamorelin is a synthetic pentapeptide, a chain of five amino acids, developed by Novo Nordisk in Denmark and described in full in 1998 (Raun 1998). It came from a series built by removing the central Ala-Trp pair from an earlier growth hormone releasing peptide, GHRP-1. Only two of its five residues, histidine and lysine, are standard building blocks of human proteins. The other three, 2-aminoisobutyric acid (Aib), D-2-naphthylalanine and D-phenylalanine, are synthetic or mirror-image forms, and the chain ends in an amide. It is not a fragment of any human hormone. It is a designed drug candidate.

Is ipamorelin a peptide or a SARM?

A peptide. SARMs are small molecules designed to act at the androgen receptor. Ipamorelin works through a different receptor entirely and belongs to a separate class, the growth hormone secretagogues.

How ipamorelin works

Ipamorelin binds the growth hormone secretagogue receptor, GHS-R1a, which is the receptor for ghrelin, a hormone made mainly in the stomach. On the somatotroph cells of the pituitary, activating that receptor releases stored growth hormone, and growth hormone in turn drives production of IGF-1, largely in the liver. Raun and colleagues used receptor antagonists to show that ipamorelin acts through this GHRP-type receptor and not through the receptor for growth hormone releasing hormone (GHRH), the hypothalamic signal that normally drives growth hormone release (Raun 1998).

Two consequences follow. First, ipamorelin does not supply growth hormone. It prompts the pituitary to release its own, as a pulse rather than a constant level. Second, GHS-R1a is not confined to the pituitary. Stimulating the ghrelin receptor also increases movement in the upper and lower gut, which is why the only published patient trial of ipamorelin was in bowel surgery rather than in growth hormone deficiency (Beck 2014).

What "selective" means

The older peptides in the family, GHRP-6 and GHRP-2, release growth hormone but also raise ACTH and cortisol, the stress-axis hormones. In conscious pigs, Raun's group found that ipamorelin released growth hormone with potency and efficacy close to GHRP-6, while its ACTH and cortisol levels did not differ significantly from those seen after GHRH, even at amounts more than 200-fold above the level needed for a half-maximal growth hormone response. None of the compounds tested changed FSH, LH, prolactin or TSH. On that basis the authors called ipamorelin the first selective growth hormone secretagogue (Raun 1998). The selectivity finding comes from pigs, and none of the published human studies was designed to test it.

What the published research reports

Healthy volunteers: a short-lived peptide

The main published pharmacokinetic study in healthy people gave 15-minute intravenous infusions to eight men at each of five infusion rates (Gobburu 1999). Blood levels rose in proportion to the amount infused, and the terminal half-life was about two hours. Each infusion produced a single episode of growth hormone release, peaking at about 40 minutes and falling back to negligible levels. The growth hormone response varied more between individuals than drug exposure did. The study measured ipamorelin and growth hormone concentrations only. It did not measure body composition, strength or any clinical outcome.

The published patient trial

Ghrelin's effect on gut movement led to a phase 2 trial in postoperative ileus, the temporary halt of gut motility after abdominal surgery (Beck 2014). The multicentre, double-blind study enrolled 117 adults having small or large bowel resection and randomised them to intravenous ipamorelin or placebo for up to seven days after the operation, with 114 analysed. Median time to tolerating a solid meal was 25.3 hours with ipamorelin and 32.6 hours with placebo, a difference that was not statistically significant (p = 0.15), and no secondary efficacy measure differed either. The authors noted that the study was small and enrolled patients with a wide range of underlying conditions.

Ipamorelin side effects: what has been recorded

In the ileus trial, treatment-emergent adverse events were reported in 87.5 per cent of the ipamorelin group and 94.8 per cent of the placebo group, and the authors described the peptide as well tolerated over the week of treatment (Beck 2014). Those figures come from one week of supervised intravenous use in patients recovering from bowel surgery, where adverse events are expected whatever the treatment. They say nothing about repeated exposure over months.

A 2026 endocrinology review of growth hormone axis peptides sold as research compounds, which groups ipamorelin with GHRP-2, GHRP-6 and hexarelin, lists the adverse effects reported across the peptides it covers: prolactin and cortisol elevations, appetite changes, dysglycaemia (abnormal blood glucose), fluid retention, muscle and joint pain, and injection-site reactions (Dominikowski 2026). It describes concerns about stimulating cell growth as biologically plausible but unproven. In the pig work, cortisol rises belonged to the older GHRPs rather than ipamorelin. No long-term human study exists, so its effect on glucose regulation and on cancer risk over extended exposure is unknown. None of these findings is a claim about any product.

Ipamorelin compared with CJC-1295, tesamorelin, sermorelin and MK-677

Comparison searches mostly mix two different mechanisms. Ipamorelin and MK-677 act at the ghrelin receptor. CJC-1295, tesamorelin and sermorelin are analogues of GHRH and act at the GHRH receptor. Both routes end at the same pituitary cells.

All five are prohibited at all times under class S2 of the WADA Prohibited List. MK-677 has by far the largest human literature of the group; the article comparing MK-677, ipamorelin and somatropin covers that pairing in detail, and the MK-677 collection lists the brands stocked.

Ipamorelin and CJC-1295

The pair is searched together because the two act at different receptors on the same pituitary cells, and the rationale offered online is that the two signals add together. At the time of writing, a PubMed search for both names returns mostly review articles and an equine anti-doping method, but no controlled human trial of the combination. Free Muscle does not publish combination guidance for any research compound.

Ipamorelin vs tesamorelin and sermorelin

The difference is receptor and evidence. Tesamorelin and sermorelin both work upstream of the ghrelin pathway, through the GHRH receptor. Tesamorelin's US licence rests on phase 3 trials, and sermorelin was used clinically in the United States for years. Ipamorelin reached phase 2 in a gut indication and showed no significant effect. They share a downstream target and little else.

Regulatory status in the UK, EU and US

Is ipamorelin legal in the UK?

Ipamorelin is not a controlled drug, and it is not a licensed medicine: the MHRA has never granted it a marketing authorisation. It is not an authorised food supplement or novel food either. Free Muscle supplies it to adults for laboratory research only, not for human consumption. A UK seller that offers dosing instructions, promises results or describes ipamorelin as a supplement risks presenting an unlicensed product as a medicine, which is regulated by the MHRA.

European Union and United States

The EMA has not authorised ipamorelin, and it is not an approved novel food in the EU. In the United States it has no FDA approval for any indication.

WADA and anti-doping tests

Ipamorelin is named in class S2 of the WADA Prohibited List among the growth hormone secretagogues that mimic ghrelin. S2 substances are prohibited at all times, in and out of competition, and UK Anti-Doping applies the list to every sport that follows the World Anti-Doping Code.

It is detectable. Anti-doping chemists in Moscow and Cologne gave ipamorelin nasally to one volunteer and collected urine for two days. Ipamorelin was heavily metabolised, and a four-residue breakdown product, ipamorelin (1-4) free acid, was still detected after the intact peptide had disappeared from the samples. The metabolites were added to routine screening, and the authors concluded that the detection window depends on individual metabolism, the preparation and the route (Semenistaya 2015). No study gives a general detection window for ipamorelin, so the accurate statement is: detectable, window not established.

Common questions

What is the ipamorelin dosage or dosage per day?

We do not publish dosing, frequency or cycle guidance for any research compound. Ipamorelin is not a licensed medicine and has no authorised dose. The amounts in the studies above were weight-based intravenous infusions given under clinical supervision, and they have no application outside those settings.

Ipamorelin benefits, muscle and results

We make no outcome claims. None of the human studies described in this guide measured muscle mass, strength or body fat. What exists is growth hormone release in animals and in small infusion groups, and one trial in surgical patients that did not meet its endpoints.

Ipamorelin tablets, capsules and pens in the UK

The human studies described here used intravenous infusion, apart from the single-volunteer nasal detection study. We have found no published oral study of ipamorelin in people. Peptides swallowed as tablets or capsules meet stomach acid and digestive enzymes before they can be absorbed, a problem set out in our article on whether oral peptides work. Pens are an injectable presentation, and no licensed ipamorelin pen exists. The Free Muscle ipamorelin listing is a capsule product, 60 capsules per bottle, supplied as batch-tested material for research, and we do not claim it reproduces the injected studies.

Ipamorelin UK reviews and Reddit reports

Forum reports cannot tell you what was in the vial or capsule, how much of it, or whether expectation explains what the writer noticed. The 2026 review points to uncertainty over product composition in unregulated supply chains (Dominikowski 2026). A useful review of a supplier talks about delivery, packaging and whether a batch certificate was supplied, not about personal results. Our supplier verification checklist sets out what to check.

How to verify a batch of ipamorelin

No regulator checks a research peptide before it reaches the buyer, and the anti-doping literature shows why that matters. When doping laboratories in Cologne and Oslo analysed black-market growth products, they found Gly-ipamorelin, ipamorelin with an extra glycine attached at its N-terminus, and confirmed its structure by high-resolution mass spectrometry and custom synthesis (Krug 2018). The same study found glycine-extended versions of GHRP-2 and GHRP-6. A product like that could show a high purity figure and still not be ipamorelin, because purity measures how much of the sample is one compound, not which compound it is.

A batch certificate worth having shows:

• A batch number that matches the one printed on the bottle.
• An identity result by mass spectrometry that matches the expected mass of ipamorelin, which is what separates it from a glycine-extended analogue or a different GHRP.
• A purity percentage by HPLC.
• The measured quantity per capsule, where the laboratory tested it.
• The laboratory's name and the test date.

Every Free Muscle-brand batch is assayed by Janoshik Analytical, an independent laboratory, and the certificate for a batch is sent on request by email. For other brands, a certificate is shown only where the manufacturer supplies one for the batch held. The lab tests page explains the request, and our guide to reading a certificate of analysis walks through each field. UK orders ship free, tracked and in plain packaging, and unopened items can be returned within 30 days; see delivery and returns.

Related reading

• Ipamorelin: every brand stocked
• Research peptides collection
• MK-677 (ibutamoren) collection
• HGH (somatropin) collection and IGF-1 LR3 collection
• MK-677 vs ipamorelin vs somatropin: three routes to the GH axis compared
• Do oral peptides actually work? The honest answer
• How to read a certificate of analysis
• How to choose a SARMs or peptide supplier in the UK

Ipamorelin is sold by Free Muscle for laboratory research use only. It is not a licensed medicine, has not been evaluated by the MHRA, EMA or FDA, is not a food supplement and is not for human consumption. Customers must be 18 or over. Nothing in this article is medical, dosing or usage advice, and the studies described do not support any claim about any product.

References

1. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-561. 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):1412-1416. 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):1527-1534. PMID: 25331030.
4. 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. PMID: 42395176.
5. 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):919-925. PMID: 25869809.
6. 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. PMID: 29864719.