Tesamorelin vs MK-677: An Approved Peptide and an Unapproved Pill
Tesamorelin is FDA-approved for HIV-related abdominal fat. MK-677 is an unapproved oral molecule with an FDA heart-failure safety flag. Not the same class.
The short version
Tesamorelin and MK-677 both aim to raise growth hormone, but they are different kinds of substance. Tesamorelin is an injected peptide with an FDA approval, for a specific condition in people with HIV. MK-677 is an oral small molecule that has never been approved, and FDA has flagged a congestive-heart-failure safety signal from the one controlled human trial it references. Neither has trial evidence for muscle building in healthy adults.
- Tesamorelin is a 44-amino-acid injected peptide. MK-677 is a small oral molecule, not a peptide at all.
- Tesamorelin is FDA-approved, for excess abdominal fat in HIV-associated lipodystrophy. MK-677 has no approval anywhere.
- FDA has flagged a heart-failure safety signal for MK-677 from a terminated hip-fracture trial.
- Human MK-677 trials used 25 mg/day orally in older adults or obese men, not young adults training for muscle.
- Both sit under the same WADA growth-hormone-releasing-factor and secretagogue section, S2.2.4, prohibited at all times.
Vendors group tesamorelin and MK-677 together as “GH boosters.” They are different kinds of substance, do not act on the same receptor, and stand in very different places with FDA.
Side by side
| Tesamorelin | MK-677 (Ibutamoren) | |
|---|---|---|
| What it is | 44-amino-acid GHRH analogue, injected | Small oral molecule, not a peptide |
| Receptor | Pituitary GHRH receptor | Ghrelin receptor (GHS-R1a) |
| Approved use | Reduction of excess abdominal fat in HIV-associated lipodystrophy | None - never FDA-approved for any indication |
| Route | Subcutaneous injection, once daily | Oral capsule or liquid, once daily |
| Human dose | 1.28 mg (label dose) | 25 mg/day (dose used in published trials, not a label) |
| Trial population | Adults with HIV and abdominal fat accumulation | Healthy adults 60-81; obese men 18-50 |
| Tested for muscle building in healthy adults? | No trial located | No trial located |
| Key safety flag | Label warnings: neoplasm risk, elevated IGF-1, fluid retention, glucose intolerance | FDA: congestive heart failure signal from a terminated hip-fracture trial |
| WADA 2026 | S2.2.4, prohibited at all times | S2.2.4, prohibited at all times |
Full pages: Tesamorelin · MK-677. Dosing detail: tesamorelin dosage · MK-677 dosage.
Different molecules, different mechanisms
Tesamorelin is the 44-amino-acid sequence of human growth hormone-releasing factor with a hexenoyl group added, given by subcutaneous injection. It acts on the pituitary’s GHRH receptor.
MK-677 is not built from amino acids the way a peptide is. It is a small organic molecule, taken orally, that researchers describe as an agonist at the ghrelin receptor (GHS-R1a). Ghrelin-mimetic peptides such as GHRP-2 and GHRP-6 use the same pathway, but MK-677 itself is chemically unrelated to any peptide. Both pathways prompt the pituitary to release growth hormone, and that is all the two compounds share mechanistically.
Evidence: approved and narrow versus unapproved and thin
Tesamorelin’s evidence is randomised and specific:
- A 12-month trial in 404 HIV-infected patients with excess abdominal fat found visceral fat fell 10.9% on tesamorelin against 0.6% on placebo over six months. Falutz 2010 - Falutz J, Potvin D, Mamputu JC et al. Effects of tesamorelin, a growth hormone-releasing factor, in HIV-infected patients with abdominal fat accumulation: a randomized placebo-controlled trial with a safety extension. J Acquir Immune Defic Syndr. 2010;53(3):311-22., in the references below
- A JAMA trial of 50 HIV-infected patients found reductions in visceral and liver fat over six months. Stanley 2014 - Stanley TL, Feldpausch MN, Oh J et al. Effect of tesamorelin on visceral fat and liver fat in HIV-infected patients with abdominal fat accumulation: a randomized clinical trial. JAMA. 2014;312(4):380-9., in the references below
- A 53-patient trial in type 2 diabetes tested safety rather than fat loss. Clemmons 2017 - Clemmons DR, Miller S, Mamputu JC. Safety and metabolic effects of tesamorelin, a growth hormone-releasing factor analogue, in patients with type 2 diabetes: A randomized, placebo-controlled trial. PLoS One. 2017;12(6):e0179538., in the references below
- A more recent analysis of 38 people with HIV on integrase inhibitors found further visceral and liver fat declines over 12 months. Russo 2024 - Russo SC, Ockene MW, Arpante AK et al. Efficacy and safety of tesamorelin in people with HIV on integrase inhibitors. AIDS. 2024;38(12):1758-1764., in the references below
Consistent findings across large trials or meta-analyses. Multiple randomised placebo-controlled trials for the approved indication: excess abdominal fat in HIV-associated lipodystrophy. The rating does not extend to body composition in healthy adults, a use no trial has tested.
MK-677’s human evidence is smaller and comes from different populations:
- A dose-ranging trial in 32 healthy adults aged 64-81 tested 2, 10 or 25 mg/day. It found 25 mg produced the largest GH and IGF-1 rise. Chapman 1996 - Chapman IM, Bach MA, Van Cauter E et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-57., in the references below
- A trial in 24 obese men aged 18-50 used 25 mg/day for 8 weeks. It found increased fat-free mass alongside a drop in total testosterone. Svensson 1998 - 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., in the references below Svensson 1999 - Svensson J, Carlsson B, Carlsson LM 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):451-6., in the references below
- The longest trial, in 65 healthy adults aged 60-81, ran 25 mg/day for up to 2 years. Fat-free mass increased without a corresponding gain in strength or function. Nass 2008 - 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., in the references below
Small or uncontrolled human studies. Too little to settle the question either way. Three published human trials, all in adults 60+ or in obese men, none measuring muscle strength or athletic performance. Separately, FDA references a hip-fracture trial stopped early over a cardiac safety signal.
Dosing, as each page states it
Tesamorelin has one dose, because it has one approved product. The Egrifta WR label states 1.28 mg injected subcutaneously once daily into the abdomen, from a vial reconstituted with the supplied diluent and used within 7 days. No other dose is approved, and the label states it is not indicated for weight loss management. Full detail: tesamorelin dosage.
MK-677 has no approved dose or label. The figure across three published human trials is 25 mg once daily, taken orally. A comparison trial found it produced the largest hormone response among 2, 10 and 25 mg. Chapman 1996 - Chapman IM, Bach MA, Van Cauter E et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-57., in the references below That is a trial dose from studies in older adults and obese men, not a recommendation, and no trial has tested it in younger adults training for muscle. Full detail: MK-677 dosage.
Who should not use either, and the main risks
Tesamorelin’s label lists these contraindications:
- Disruption of the hypothalamic-pituitary axis.
- Active malignancy.
- Known hypersensitivity.
- Pregnancy.
Its warnings cover increased risk of neoplasms, elevated IGF-1, fluid retention, glucose intolerance or new diabetes, and hypersensitivity reactions.
MK-677 has no FDA-reviewed contraindication list, because it has never gone through that review. FDA’s bulk drug substance safety listing cites a randomised, placebo-controlled hip-fracture recovery trial that was terminated early over a heart-failure signal. It states ibutamoren mesylate “poses significant safety risks due to the potential for congestive heart failure in certain patients.”
The trials above also report a fasting glucose increase Chapman 1996 - Chapman IM, Bach MA, Van Cauter E et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-57., in the references below, reduced insulin sensitivity in the two-year trial Nass 2008 - 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., in the references below, and reduced total testosterone in obese men. Svensson 1999 - Svensson J, Carlsson B, Carlsson LM 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):451-6., in the references below Anyone with a personal or family history of heart failure, cardiac risk factors or diabetes should treat the FDA signal as a reason for particular caution.
Regulatory status
Tesamorelin
US legal status - FDA-approved · prescription only
FDA-approved as EGRIFTA WR for the reduction of excess abdominal fat in HIV-infected adult patients with lipodystrophy. Requires a prescriber. Grey-market vials carry the name without the approval, the quality control or the indication.
MK-677
US legal status - Research use only
Never FDA-approved for any indication. DailyMed's only ibutamoren mesylate listing is a bulk-ingredient powder for animal drug compounding, not a human drug product. FDA placed it in category 2 of its bulk drug substance compounding policies under both 503A and 503B.
Sport
Both compounds sit in the same subsection of the WADA Prohibited List, S2.2.4 (growth hormone releasing factors). Tesamorelin is listed among GHRH analogues, and ibutamoren/MK-677 among growth hormone secretagogues and mimetics. Both are prohibited at all times, in and out of competition, and a prescription for tesamorelin does not change that.
What the comparison tells you
One of these is an approved medicine with a label, a prescriber and a narrow, trial-tested use. The other is an unapproved oral molecule sold in the same “GH-boosting” category, with a specific FDA cardiac safety flag attached to the one controlled human trial it references. Grouping them as interchangeable “GH peptides” hides how different their regulatory status and risk profiles are. MK-677 is not a peptide at all.
Related
Common questions
Is tesamorelin the same as MK-677?
No. Tesamorelin is an injected 44-amino-acid peptide, a growth hormone-releasing hormone analogue. MK-677 (ibutamoren) is a small molecule taken as a pill or liquid that acts on a different receptor, the ghrelin receptor. Both aim to raise growth hormone, but they are chemically unrelated.
Which is safer, tesamorelin or MK-677?
Tesamorelin has an FDA-reviewed safety and prescribing profile for its approved use, with a prescriber managing contraindications and monitoring. MK-677 has never been through that review. FDA has published a specific safety flag: a controlled hip-fracture trial of ibutamoren mesylate was stopped early over a possible link to congestive heart failure. Neither profile applies to unsupervised use outside their studied populations.
Can I use tesamorelin or MK-677 for muscle building?
Neither has trial evidence for that in healthy adults. Tesamorelin's trials are in adults with HIV-associated lipodystrophy, measuring visceral fat, and its label states it is not indicated for weight loss management. MK-677's published trials are in adults aged 60-81 and in obese men, and none measured muscle strength or athletic performance.
References (11 sources)
Bibliographic detail is fetched from PubMed, not written by me - so a citation here cannot drift from the paper it names. Study design comes from PubMed's own tags rather than my judgement.
- 1.Falutz J, Potvin D, Mamputu JC et al. Effects of tesamorelin, a growth hormone-releasing factor, in HIV-infected patients with abdominal fat accumulation: a randomized placebo-controlled trial with a safety extension. J Acquir Immune Defic Syndr. 2010;53(3):311-22.Randomised trialPMID 20101189
- 2.Stanley TL, Feldpausch MN, Oh J et al. Effect of tesamorelin on visceral fat and liver fat in HIV-infected patients with abdominal fat accumulation: a randomized clinical trial. JAMA. 2014;312(4):380-9.Randomised trialPMID 25038357full text
- 3.Clemmons DR, Miller S, Mamputu JC. Safety and metabolic effects of tesamorelin, a growth hormone-releasing factor analogue, in patients with type 2 diabetes: A randomized, placebo-controlled trial. PLoS One. 2017;12(6):e0179538.Randomised trialPMID 28617838full text
- 4.Russo SC, Ockene MW, Arpante AK et al. Efficacy and safety of tesamorelin in people with HIV on integrase inhibitors. AIDS. 2024;38(12):1758-1764.Randomised trialPMID 38905488full text
- 5.Chapman IM, Bach MA, Van Cauter E et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-57.Randomised trialPMID 8954023
- 6.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.Randomised trialPMID 18981485full text
- 7.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.Randomised trialPMID 9467542
- 8.Svensson J, Carlsson B, Carlsson LM 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):451-6.Randomised trialPMID 10468903
- 9.EGRIFTA WR (tesamorelin) - current prescribing information on DailyMed: indication, dosage of 1.28 mg subcutaneously once daily, and the statement that it is not indicated for weight loss management.- DailyMed, National Library of Medicinelabel
- 10.FDA - Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Ibutamoren mesylate entry: congestive heart failure signal from a terminated hip-fracture trial, category 2 under 503A and 503B.- US Food and Drug Administrationregulatory
- 11.JADCO 2026 Prohibited List (WADA mirror, PDF) - section S2.2.4, growth hormone releasing factors, naming both tesamorelin (GHRH analogues) and ibutamoren/MK-677 (GH secretagogues and mimetics) as prohibited at all times.- World Anti-Doping Agency (mirrored by the Jamaica Anti-Doping Commission)regulatory