MK-677 (Ibutamoren) Capsules UK

MK-677, also known as ibutamoren, ibutamoren mesylate, MK-0677, L-163,191 and Nutrobal, is a non-peptide growth hormone secretagogue: an orally active small molecule that acts as an agonist at the ghrelin receptor, GHS-R1a. This page lists every brand of MK-677 stocked at Free Muscle, our own Janoshik batch-tested capsules alongside iMuscle, Yakka Strength and Thoroughbred Labs, compared on strength per capsule, pack size and batch testing. Everything here is supplied for laboratory research only, to adults aged 18 or over.

What is MK-677?

MK-677 belongs to the growth hormone secretagogue class. It was developed at Merck in the 1990s as an orally available, non-peptide mimic of the growth hormone releasing peptides such as GHRP-6, which are only active by injection. It binds and activates the growth hormone secretagogue receptor (GHS-R1a) in the pituitary and hypothalamus, the same receptor that the stomach hormone ghrelin acts on. In trial participants, this amplified the pulsatile release of growth hormone and raised circulating insulin-like growth factor 1 (IGF-1) levels.

It is worth being precise about what MK-677 is not. It is not a SARM, not an anabolic steroid, not a peptide and it contains no growth hormone. It is unusual among research compounds sold in the UK in having a substantial published human trial record, including studies in older adults, obese men, patients recovering from hip fracture and patients with Alzheimer disease. Despite that record, it was never approved as a medicine anywhere in the world, and clinical development was discontinued.

Ibutamoren exists in two forms that are easy to confuse: the free base and its methanesulfonate (mesylate) salt. Labels do not always say which form they mean, and several trial reports, including the hip fracture and Alzheimer trials, name the mesylate salt. Identifiers below are from PubChem, checked in October 2026.

What the published research reports

In a two-year randomised, placebo-controlled trial in 65 healthy adults aged 60 to 81 (Nass et al., 2008), MK-677 raised growth hormone and IGF-1 into the range seen in young adults. Fat-free mass rose by about 1.1 kg in the MK-677 group against a fall of 0.5 kg on placebo, and body weight rose by 2.7 kg against 0.8 kg. Abdominal visceral fat and total fat mass did not change, but limb fat increased more in the treated group. Fasting glucose rose, insulin sensitivity fell, cortisol increased, and the most frequent side effects were increased appetite, transient lower-limb oedema and muscle pain. The extra fat-free mass did not translate into any change in strength or function.

In an eight-week trial in 24 obese men (Svensson et al., 1998), serum IGF-1 rose by roughly 40 per cent and fat-free mass increased, while total and visceral fat were unchanged. Basal metabolic rate rose at two weeks but not at eight, and an oral glucose tolerance test showed impaired glucose handling at both time points.

A phase IIb study in 123 elderly patients recovering from hip fracture (Adunsky et al., 2011) reported higher IGF-1 and improved gait speed, but stair-climbing power did not differ significantly from placebo and most other measures of physical function showed no improvement. The trial was terminated early because of a safety signal of congestive heart failure in a small number of patients, and the authors concluded that the compound had an unfavourable safety profile in that population.

A small study measured sleep (Copinschi et al., 1997). In eight young adults, each given placebo and two dose levels for seven days in random order, stage IV sleep lasted about 50 per cent longer and REM sleep more than 20 per cent longer than on placebo at the higher level. Six adults aged 65 to 71 showed nearly 50 per cent more REM sleep than at baseline, without a placebo period. Both groups were very small.

In an 18-month trial in 292 women aged 64 to 85 with postmenopausal osteoporosis (Murphy et al., 2001), MK-677 increased markers of bone formation as well as bone breakdown; added to alendronate, it raised bone mineral density at the femoral neck by 4.2 per cent against 2.5 per cent on alendronate alone, but not at the lumbar spine, total hip or whole body. Growth hormone related side effects were recorded, and the authors judged the lack of gain at other sites a concern when weighed against them.

None of these findings is a claim about the products listed on this page. They describe what was measured in specific trial populations under medical supervision, and they include the adverse findings for a reason.

Brands of MK-677 we stock

• Free Muscle MK-677 Ibutamoren: our own brand, capsules, 60 per bottle, in three strengths: 10mg, 12.5mg and 25mg. Every batch is assayed for identity and purity by Janoshik Analytical, with the Certificate of Analysis sent on request. The three strengths have their own page at Free Muscle MK-677 Ibutamoren.
• iMuscle Ibutamoren MK-677: 10mg per capsule, 60 capsules, 600mg total per pack. A COA is shown where iMuscle supplies one for the batch we hold.
• Yakka Strength MK-677: 60 capsules. Yakka Strength states 10 mg per capsule, which is 600 mg per pack. A COA is shown where Yakka Strength supplies one for the batch we hold.
• Thoroughbred Labs MK-677: 60 capsules. Thoroughbred Labs states 12.5 mg per capsule, which is 750 mg per pack. A COA is shown where Thoroughbred Labs supplies one for the batch we hold.
• MK-777 (Acetamoren) Bioreactive Series: a Free Muscle product designation from our Bioreactive Series, 60 capsules, Janoshik batch-tested. MK-777 is not a name found in the published pharmacological literature, so it is compared on its own page at MK-777 rather than treated as an MK-677 equivalent.

How to compare them

Two bottles of 60 capsules can contain very different quantities of compound. Multiply the strength per capsule by the number of capsules to get total milligrams per pack: 10mg x 60 is 600mg, 12.5mg x 60 is 750mg, 25mg x 60 is 1,500mg. Divide the price on the listing by that total to get a cost per milligram, which is the only like-for-like comparison between brands. Then check whether a batch certificate exists for the exact batch on the label, because an untested 25mg capsule is not worth more than a tested 10mg one. Our article MK-677 by brand walks through the same arithmetic. One further check is specific to MK-677: a stated strength may refer to ibutamoren itself or to the heavier mesylate salt, which is about 85 per cent ibutamoren by mass, so two listings that both say 10mg can differ by roughly 15 per cent in actual ibutamoren. The certificate should say which basis it uses, and our 12.5mg listing works through the numbers.

At the prices on 16 October 2026, the Free Muscle 25mg bottle (25mg × 60 = 1,500mg for £69.99, or £1.17 per capsule) works out at £0.047 per mg, the lowest price per milligram of the MK-677 listings on this page that state a strength. The others, per mg: Thoroughbred Labs 12.5mg £0.052, Free Muscle 12.5mg £0.060, iMuscle 10mg £0.078, Free Muscle 10mg £0.083 and Yakka Strength 10mg £0.093. Prices change, so the comparison table above always shows the current figures.

Batch testing and certificates of analysis

A Certificate of Analysis (COA) is a laboratory report on one specific batch. For MK-677 it should show the identity of the compound (usually by HPLC or mass spectrometry against a reference standard), the measured purity as a percentage, the batch number, the date of testing and the name of the laboratory. Every Free Muscle brand batch is assayed by Janoshik Analytical, an independent laboratory; email us with the batch number printed on your label and we send the certificate for that batch. For iMuscle, Yakka Strength and Thoroughbred Labs, a COA is shown on the listing only where the manufacturer supplies one for the batch we hold. A generic PDF with no batch number, or a certificate for a batch that is not the one in your hand, is marketing rather than evidence. See how we test and how to read a COA.

Where to buy MK-677 in the UK: how to check a supplier

Whichever shop you buy MK-677 from, check these five points before you order:

1. A batch number and a certificate for that batch. The pack should carry a batch number, and the seller should be able to show a certificate of analysis for that same batch from a named laboratory, with the test date. Every Free Muscle-brand batch is assayed by Janoshik Analytical, and we send the certificate for your batch on request. For iMuscle, Thoroughbred Labs and Yakka Strength, a certificate is shown where the brand supplies one for the batch we hold.
2. The strength per capsule and the capsule count. With both figures you can work out the total milligrams in the pack and the price per milligram; the comparison table above does this for every listing here that states both. If a listing does not state one of them, ask the seller before you order.
3. Research-use labelling and an age check. A research compound should be sold for laboratory research use only, not for human consumption, to adults aged 18 or over, with no dosing or usage advice. That is how every listing here is sold.
4. Prices in pounds sterling and tracked UK dispatch. UK delivery from us is free and tracked on every order, with no minimum spend, and usually arrives 2-3 working days after dispatch; orders placed before 2pm Monday to Friday are processed the same working day.
5. A clear returns policy. Unopened items can be returned to us within 30 days.

Brands on this page: Free Muscle, iMuscle, Thoroughbred Labs and Yakka Strength. The UK supplier checklist and how we test go into more detail.

Legal status in the UK

Ibutamoren is not listed under the Misuse of Drugs Act 1971, so it is not a controlled drug; the restrictions on it come from medicines and food law instead. MK-677 is not a licensed medicine in the UK and has no marketing authorisation from the MHRA. It is not an authorised food supplement or novel food, and it cannot be sold for human consumption. Free Muscle supplies it as a research compound for laboratory use only, to customers aged 18 or over. Growth hormone secretagogues, including ibutamoren, are prohibited at all times under section S2 of the WADA Prohibited List, the list UK Anti-Doping enforces across UK sport, so it is not compatible with drug-tested sport. Full detail is on our MK-677 legal status in the UK page.

Storage and handling

Keep capsules in the original sealed container, in a cool, dry place away from direct light and heat. Reseal after opening and do not decant into unlabelled containers. Keep out of the reach of children and pets. Handle in line with normal laboratory good practice, record the batch number for any work you carry out, and dispose of unwanted material responsibly.

Delivery and returns

Free Muscle is the trading name of FreeMuscle, a business registered in Andorra, with UK operations and dispatch in Scunthorpe. Every order ships with free tracked UK delivery in plain packaging, and orders placed before 2pm Monday to Friday are processed the same working day. EU delivery takes 3 to 7 working days. Unopened items can be returned within 30 days. See delivery and our 30-day guarantee.

Related reading

• MK-677 (Ibutamoren): What the Research Says
• MK-677 by brand: what actually differs when the molecule is the same
• Price per milligram: the only honest way to compare SARMs and peptides
• What Is Janoshik Analytical? Third-Party Testing Explained
• How to choose a SARMs or peptide supplier in the UK: a checklist

• Free Muscle MK-677 Ibutamoren (10mg, 12.5mg, 25mg)
• MK-777 (Acetamoren)
• Ipamorelin
• SARMs

References

• Nass R, 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):601-611. PMID: 18981485.
• Svensson J, 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):362-369. PMID: 9467542.
• Adunsky A, et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr. 2011;53(2):183-189. PMID: 21067829.
• Sevigny JJ, et al. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology. 2008;71(21):1702-1708. PMID: 19015485.
• Copinschi G, et al. Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man. Neuroendocrinology. 1997;66(4):278-286. PMID: 9349662.
• Murphy MG, et al. Effect of alendronate and MK-677 (a growth hormone secretagogue), individually and in combination, on markers of bone turnover and bone mineral density in postmenopausal osteoporotic women. J Clin Endocrinol Metab. 2001;86(3):1116-1125. PMID: 11238495.
• Svensson J, et al. Discrepancy between serum leptin values and total body fat in response to the oral growth hormone secretagogue MK-677. Clin Endocrinol (Oxf). 1999;50(4):451-456. PMID: 10468903.

Last reviewed: October 2026.

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.

Research guides

• MK-677 vs ipamorelin vs HGH: three routes to the GH axis compared
• MK-777 (Acetamoren): what the name means and how it relates to MK-677
• Is HGH legal in the UK? Somatropin, prescriptions and the law
• MK-677 side effects reported in human trials, study by study
• Ibutamoren UK: can you buy it? Law, lab testing and how orders work
• All research guides