A Lifter's Guide to Peptide Families: From Growth Hormone to Injury Repair

Why 'Peptide' Is Too Vague a Term

A peptide is a short chain of amino acids. That definition covers insulin and the semaglutide in Wegovy, so the word alone says little about what a compound does.

In lifting circles, "peptides" usually means signaling molecules sold online for "research use only" and used for body composition or recovery. They fall into a handful of families that act on different receptors and carry different risks.

A few have small human studies; many have only rodent or cell data. This page sorts the main families by what each is reported to do and labels the evidence behind it. For what the "research use only" label means legally, start with our hub on the legal status of peptides.

Growth Hormone Secretagogues and GHRH Analogues

These growth hormone secretagogues prompt the pituitary gland to release more of the body's own growth hormone (GH) instead of supplying GH from outside. Users often combine the two groups below.

GHRHs (The Gas Pedal)

Growth hormone-releasing hormone (GHRH) analogues bind the GHRH receptor on pituitary cells and boost GH release. Mod GRF 1-29, often sold as "CJC-1295 without DAC," is short-acting. CJC-1295 with DAC carries a drug affinity complex that binds albumin in the blood. In 2006 trials in healthy adults, its half-life was 5.8-8.1 days, and one injection raised mean GH 2- to 10-fold for at least six days.

Forum guides often say the DAC version causes a constant "GH bleed" with no real pulses. The one human study that measured this found otherwise. Researchers sampled blood every 20 minutes overnight in healthy men before and one week after a single 60 or 90 mcg/kg injection. Pulse frequency and size didn't change. What rose was the floor between pulses: trough GH went up about 7.5-fold, while mean GH rose 46% and IGF-1 45%. Nobody has tested whether that higher trough changes results or side effects over months.

GHRPs (The Ignition Switch)

Growth hormone-releasing peptides (GHRPs) act on the ghrelin receptor (GHS-R1a), so they're also called ghrelin mimetics. They trigger GH release directly, and researchers in 1990 proposed that they also counter somatostatin, the hormone that holds GH back. In a 1990 study of 18 healthy men, low IV doses of GHRP-6 given with GHRH released more GH than either would alone, which is the rationale for stacking the two groups.

The members differ mainly in side effects:

• GHRP-6 is the oldest. Prolactin and cortisol roughly doubled at the top dose in that 1990 study. Users commonly report strong hunger soon after injecting.
• GHRP-2 (pralmorelin) is similar. A 1998 swine study found that both it and GHRP-6 raised ACTH and cortisol. Users generally describe less hunger than with GHRP-6.
• Ipamorelin is the one vendors market as "clean." In that swine study it released GH without raising ACTH or cortisol, even at very high doses. FDA's 2024 review lists one IV study in 48 healthy men and a Phase 2 trial in 117 adults after bowel surgery. That trial missed its primary endpoint. The ipamorelin group had more low potassium and high blood sugar than placebo, plus two deaths; FDA reviewers said it's unclear whether ipamorelin played a role. Users say it causes little hunger; we found no human study measuring appetite. The site rates its evidence as moderate.

No controlled trial has tested a GHRH-plus-GHRP stack for muscle or fat outcomes; the common protocols come from forums, as our page on reported dosing protocols explains.

The Repair Crew: Peptides for Healing and Recovery

Lifters often pair BPC-157 and TB-500 for tendon and muscle injuries. Almost everything known about both comes from animal and cell studies.

BPC-157 is a synthetic peptide based on a protein in human gastric juice. A 2025 systematic review found 36 eligible studies, 35 of them preclinical. In animal injury models, from torn tendons to fractures, it improved healing, apparently in part through angiogenesis and reduced inflammation. The only human data came from a small retrospective series in which 7 of 12 people with chronic knee pain reported relief after a knee injection. The reviewers found no clinical safety data. The site rates BPC-157's evidence as emerging.

TB-500 isn't the full thymosin beta-4 (Tβ4) protein. In 2012, anti-doping chemists in Ghent identified the active ingredient of a TB-500 product as Ac-LKKTETQ, a seven-amino-acid fragment (residues 17-23) of the 43-amino-acid Tβ4. The human trials people cite, such as eye-drop studies, used full Tβ4. As of October 2026, FDA says it has found no human exposure data for the fragment. The idea that TB-500 works "systemically" while BPC-157 works locally comes from vendors and forums, not from studies. The site rates TB-500's evidence as preliminary; see what's known about recovery peptides in people.

Fat-Loss Peptides

AOD-9604 is a modified growth hormone fragment (amino acids 177-191 plus an extra tyrosine) developed to keep GH's fat-burning effect without raising IGF-1. Its human trials all used oral or IV dosing. The largest, the OPTIONS trial in 536 adults with obesity, tested oral doses of 0.25-1 mg daily and found no significant weight loss versus placebo at 12 weeks, according to FDA's 2024 review. There are no human data on injected AOD-9604, which is how users take it.

Semaglutide and tirzepatide are peptides too: approved prescription medicines backed by large Phase 3 trials, and by far the best-studied fat-loss peptides. Our fat-loss comparison covers the numbers. Research-use vials sold under those names aren't the same as the prescription products.

Melanocortins: Tanning and Libido

Melanotan II is a synthetic analogue of alpha-melanocyte-stimulating hormone (alpha-MSH) that acts on melanocortin receptors. In a 1996 pilot in three healthy men, five low subcutaneous doses darkened the skin of two. Mild nausea was common, and spontaneous erections followed dosing. In a 1998 crossover trial, 8 of 10 men with psychogenic erectile dysfunction had erections on melanotan II. Nausea and yawning were more common than on placebo.

It isn't approved anywhere. FDA cites published case reports of serious events such as melanoma and priapism. Users commonly describe new or darker moles. A related drug, bremelanotide (PT-141), is FDA-approved as Vyleesi, but only for low sexual desire in premenopausal women.

Nootropic Peptides

Semax and Selank were developed in Russia, where both are registered as nasal drops. The human evidence is mostly small Russian studies without placebo controls. In one 1997 study, 30 stroke patients given Semax at 12-18 mg a day alongside standard care recovered neurological function somewhat faster than 80 patients on standard care alone. Neither is approved in the US or EU, and we found no controlled study in healthy people. The site rates Semax's evidence as moderate.

Dihexa is often described online as helping form new connections between neurons, a claim based on Washington State University rat and cell work. In April 2025 the Journal of Pharmacology and Experimental Therapeutics retracted the 2014 paper tying dihexa's effects to the HGF/c-Met system, after a university investigation found falsified or fabricated data. A related 2012 paper was retracted at the same time. As of October 2026, FDA says it has found no human exposure data for dihexa.

The Lay of the Land: A Cheat Sheet

Where the Families Stand in Sport and Law

As of October 2026, WADA's 2026 Prohibited List covers nearly every family here:

• S0 (non-approved substances): BPC-157 by name. Melanotan II and dihexa aren't named but appear to fall under S0's catch-all for unapproved substances (our reading).
• S2.2.3 (GH fragments): AOD-9604 and hGH 176-191.
• S2.2.4 (GH-releasing factors): CJC-1295, ipamorelin, GHRP-2/-6 and hexarelin.
• S2.3 (growth factors): thymosin beta-4 and its derivatives such as TB-500, and IGF-1 with its analogues.
• Monitoring Program only: semaglutide and tirzepatide.

We couldn't confirm how WADA treats Semax and Selank, which are registered medicines in Russia. BPC-157 never slipped past the list for being novel; S0 exists for that kind of compound. Our page on peptides in sport covers testing and penalties.

In the US, none of the research peptides here is an approved drug. As of October 2026, FDA's page on bulk substances that may carry significant safety risks says the agency has found no human exposure data for TB-500 or dihexa, and limited safety information for BPC-157.