What "muscle growth peptide" actually means
None of the compounds grouped under this label build muscle directly. They are signalling molecules. The largest group nudges the pituitary into releasing more of the growth hormone it already makes; a second group is studied for connective-tissue repair, which touches training only through recovery. Neither is an anabolic steroid, and neither substitutes for the mechanical tension, protein intake and sleep that drive hypertrophy in the first place.
This distinction matters because the marketing collapses it. A compound with a measurable effect on a blood hormone is not the same as a compound with a measurable effect on lean mass, and the second claim requires a trial that in most of these cases has never been run.
The growth hormone axis in plain terms
The hypothalamus releases GHRH, which tells the pituitary to release growth hormone in pulses. Somatostatin is the brake on that system, and ghrelin — the same hormone associated with hunger — acts on a separate receptor that amplifies the pulse. Growth hormone then drives the liver to produce IGF-1, which is the signal most closely associated with tissue growth.
Secretagogues work on that chain rather than replacing it. GHRH analogues such as CJC-1295 and tesamorelin imitate the upstream signal. Ghrelin-receptor agonists such as ipamorelin act on the second receptor. Because both preserve the body's pulsatile pattern and its negative feedback, they behave differently from injected recombinant growth hormone — which is a prescription medicine, and a different conversation.
Raising GH and IGF-1 is measurable. Translating that into lean mass in a healthy, trained adult is the step the evidence does not currently cover.
The compounds, and where each one stands
Each entry links to a full profile with mechanism, half-life, side-effect profile, storage, legal status and references.
- CJC-1295Moderate evidence
A GHRH analogue that raises endogenous growth hormone and IGF-1 output. Human pharmacokinetic studies confirm the hormonal effect; body-composition trials in healthy trained adults are what is missing.
- IpamorelinModerate evidence
A selective ghrelin-receptor agonist that triggers GH pulses without meaningfully moving cortisol or prolactin. Frequently paired with a GHRH analogue because the two act on different receptors.
- TesamorelinStrong evidence
The only GHRH analogue on this page with regulatory approval, licensed for HIV-associated lipodystrophy. Its trial record is about visceral fat, not hypertrophy in healthy athletes.
- BPC-157Emerging evidence
A synthetic peptide studied for tendon, ligament and gut healing in rodents. Relevant to training only through recovery; there are no controlled human hypertrophy data.
- TB-500Emerging evidence
A thymosin beta-4 fragment studied for cell migration and tissue repair. Same category as BPC-157: a recovery hypothesis, animal evidence, no human trials in athletes.
- MOTS-cEmerging evidence
A mitochondrial-derived peptide studied for AMPK signalling and exercise capacity in mice. Metabolic rather than anabolic, and preclinical throughout.
Reading the evidence grades
Strong means multiple randomised, placebo-controlled human trials plus regulatory review. Moderate means real human data at a smaller scale. Emerging means convincing preclinical work with human studies barely started. Limited means animal or in-vitro work only.
Read the grade against the claim being made. Tesamorelin is graded Strong, but its trials measured visceral fat in a specific patient population — that record says nothing about hypertrophy in a healthy lifter. A high grade for one endpoint is not a high grade for every endpoint.
The safety and evidence guide works through how to interrogate a claim: was it in humans, was it randomised and controlled, and has anyone reproduced it.
Recovery is not the same claim as growth
BPC-157 and TB-500 dominate this category online, yet neither has a proposed anabolic mechanism. The research interest is in angiogenesis, cell migration and tendon or ligament repair, almost entirely in rodents. The implied training argument — recover faster, train more, grow more — is plausible and untested, and the intermediate step it depends on has not been demonstrated in humans.
Approved medicine versus research chemical
Tesamorelin is a licensed product: a known manufacturer, a verified concentration, a printed label, a sterility standard and a regulator that can recall it. Everything else on this page is typically sold "for research purposes only", which means purity, identity, sterility and the actual quantity in the vial are unverified. A certificate of analysis describes one batch at one moment, and can be fabricated.
Several of these compounds are also on the WADA prohibited list, so anyone in a tested sport should check current status before anything else.
Things this page deliberately does not say
- Which compound is best. That depends on a medical history this site cannot see.
- How much anyone should take, or how to stack anything. That belongs to a prescriber.
- How much muscle anyone will gain. No trial supports a number for healthy trained adults.
- Where to buy anything. This site lists no vendors and takes no affiliate revenue.
Growth hormone secretagogues affect insulin sensitivity, fluid balance and, in theory, the growth of tissue you would rather not grow. Anyone considering them should be talking to a clinician who can review their history. See the full disclaimer.