The short answer: the "15%" people quote for tesamorelin is real, but it comes from trials in adults with HIV and a fat-redistribution condition, measured as visceral (deep belly) fat over 26 weeks. Ipamorelin, the other half of the popular stack, has never been tested in people for body composition. Neither has the combination.
That doesn't make the stack useless. It means most of what you read about it is mechanism, animal data and anecdote, sold with one borrowed number.
Status as of October 25, 2026: tesamorelin is FDA-approved only as Egrifta, for excess abdominal fat in adults with HIV and lipodystrophy. Ipamorelin isn't approved for any use. No trial has tested the two together. This post describes the published evidence. It isn't medical advice.
Updated Oct 25, 2026: this is the web version of a September 14, 2026 email. The 15% figure, the ipamorelin evidence and FDA's status lists were re-checked against the sources linked below.
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What is the tesamorelin and ipamorelin stack?
It pairs two compounds that push growth hormone release through two different receptors.
Tesamorelin is a lab-made version of growth hormone-releasing hormone (GHRH). The Egrifta label says it binds the GHRH receptor on the pituitary and stimulates "the synthesis and pulsatile release of endogenous growth hormone" (Egrifta WR label, rev. 3/2025). In other words, your own GH, in pulses, not injected GH.
Ipamorelin works on a different receptor, the ghrelin receptor (also called the growth hormone secretagogue receptor). Its developers described it in 1998 as "the first selective growth hormone secretagogue" (Raun et al., Eur J Endocrinol, 1998).
The logic of pairing them is that two separate signals might add up. That's a reasonable idea from the biology. It's also the part nobody has tested in this pair. The two receptor families are explained side by side in GHRH vs GHS.
Where does the 15% number come from?
It comes from the tesamorelin Phase 3 trials in HIV-associated lipodystrophy, the drug's only FDA approval.
The first trial, published in the New England Journal of Medicine, enrolled 412 adults with HIV and excess belly fat, 86% of them men. After 26 weeks, "visceral adipose tissue decreased by 15.2% in the tesamorelin group and increased by 5.0% in the placebo group" (Falutz et al., NEJM, 2007).
The label reports both trials. Visceral fat changed by -18% vs +2% on placebo in one and -14% vs -2% in the other. Body weight didn't change meaningfully in either. The label says tesamorelin "is not indicated for weight loss management as it has a weight neutral effect" (Egrifta WR label).
Three things get lost when the number travels:
The population. Adults with HIV and lipodystrophy, ages 18 to 65, mostly men around 48.
The measure. Visceral fat on a CT scan, not body weight or the number on the scale.
What happened after. In the extension, people switched to placebo regained visceral fat (+22% and +16% between weeks 26 and 52, per the label).
There is one placebo-controlled trial outside HIV. In 60 adults with abdominal obesity, selected for low GH output and capped at age 55, visceral fat fell 16 cm² on tesamorelin and rose 19 cm² on placebo over 12 months (Makimura et al., JCEM, 2012). That's a real signal in a narrow group. It isn't the 15%, and it isn't an approval.
The full tesamorelin picture (fatty liver, people over 50, side effects, cost) is in tesamorelin explained.
Has ipamorelin been tested in humans?
Yes, but not for what it's sold for. It's been tested in people for how the body handles it and for gut recovery after surgery. It has never been tested in people for muscle, fat or body composition.
Here's everything I found:
Human dosing study (1999). Healthy male volunteers got short IV infusions at five dose levels, eight men per level. Ipamorelin raised GH in a single peak, and the study modeled how long it lasts in the blood (Gobburu et al., Pharm Res, 1999). No body-composition measures.
Phase 2 trial after bowel surgery (published 2014). 114 adults recovering from bowel resection got IV ipamorelin or placebo. Median time to tolerating a solid meal was 25.3 hours vs 32.6 hours, and the difference wasn't statistically significant (p = 0.15) (Beck et al., Int J Colorectal Dis, 2014).
A second, larger Phase 2 gut trial. It enrolled 320 people and finished in 2014, and no results have ever been posted (ClinicalTrials.gov NCT01280344). I couldn't find a publication.
A PubMed search for "ipamorelin" returns 55 records. None is a human trial with a muscle, fat or body-composition endpoint. The body-composition work is in rats. A search for tesamorelin plus ipamorelin returns seven 2026 review articles and no trial. ClinicalTrials.gov lists no study of the combination.
Is ipamorelin really "clean"?
That reputation comes from animals. In the 1998 paper, ipamorelin released GH in rats and pigs without meaningfully raising ACTH or cortisol, even at very high doses, and without moving prolactin and other pituitary hormones (Raun et al., 1998).
That's a solid finding in animals. It hasn't been shown in a human trial built to test it. The human dosing study measured GH, not cortisol.
FDA's own read is cautious. Its compounding safety page says ipamorelin acetate may carry an immunogenicity risk for some routes, contains unnatural amino acids, and that "a study published in literature identified serious adverse events including death when ipamorelin" was given intravenously for gut motility. FDA adds that it has no safety data for other injectable routes. Ipamorelin acetate sits in Category 2 of FDA's interim policy for outsourcing facilities, and its compounding nomination is listed as withdrawn (FDA, current as of Apr 22, 2026). For where other peptides stand, see the compounding status tracker.
What does the evidence actually cover?
Claim you'll see | Where it comes from | Who was studied | What it shows, and doesn't |
|---|---|---|---|
Tesamorelin cuts belly fat 15% | Falutz 2007 NEJM; Egrifta label | Adults with HIV and lipodystrophy, 26 weeks | Visceral fat on CT fell vs placebo. Weight didn't change. Fat returned after stopping. |
Tesamorelin works without HIV | Makimura 2012 JCEM | 60 adults with abdominal obesity and low GH, age 55 or under, 12 months | Visceral fat fell vs placebo. One trial, narrow group, not approved. |
Ipamorelin releases GH | Gobburu 1999 | Healthy young men, single IV doses | GH rises in one peak. No body-composition data. |
Ipamorelin is "clean" | Raun 1998 | Rats and pigs | No cortisol or prolactin rise in animals. Not tested in a human trial. |
Ipamorelin builds muscle or burns fat | No human trial found | n/a | Animal data and anecdote only. |
The two work better together | No trial found | n/a | A rationale from two receptors. Untested in this pair. |
Is the tesamorelin ipamorelin blend legal?
Tesamorelin is a prescription drug for one use. Ipamorelin isn't approved for anything. A pre-mixed blend of the two isn't an approved product.
FDA has also named the blend specifically. In an August 24, 2026 warning letter to an online peptide seller, FDA listed a "Tesamorelin Ipamorelin Blend" among "unapproved new drugs" and said the site's own content "establishes that your products are intended to be drugs for human use", whatever the research-use label said (FDA warning letter, Aug 24, 2026).
So what's real here?
Three layers, and they're all true at once:
Real: the biology. Two receptors, two separate ways to signal GH release. Tesamorelin's effect on visceral fat in its trial populations.
Unproven: anything about ipamorelin and body composition in people, and anything about the combination.
Sleight of hand: a number from HIV lipodystrophy trials quoted as if it applies to everyone, attached to a stack that was never tested.
The stack isn't the problem. The problem is when someone quotes you the 15% and doesn't say which layer it came from. For how GH-axis peptides fit together more broadly, read your GH stack, explained honestly.
For research-grade context only, here's how I pick a peptide vendor.
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Seen someone quote the 15% to sell this stack? Reply and tell me where. I'm collecting them.