Peptides are a family of substances whose molecules are built from residues of α-amino acids, connected in a chain by peptide (amide) bonds. These are natural or synthetic compounds containing tens, hundreds or thousands of monomeric links - amino acids. This class is very diverse and performs a variety of regulatory functions in the body. In this article, we will only consider those peptides that are used in sports to correct physical indicators.
In the context of bodybuilding, "peptides" usually refer to three functional groups. The first is growth hormone secretagogues (GHRH analogs and GHRP), which stimulate the pituitary gland to release its own growth hormone. The second is peptides for tissue recovery and repair, such as BPC-157 and TB-500, used for tendon and ligament injuries. The third is peptides for reducing fat mass, the most famous of which is AOD-9604, a fragment of the growth hormone molecule.
How do growth hormone secretagogues work?
Growth hormone secretagogues (GH secretagogues) are compounds that stimulate the pituitary gland to release endogenous growth hormone, instead of introducing it from outside. They are divided into two main classes, working through different receptors, so they are often used together for synergy.
The first class is GHRH analogs (growth hormone-releasing hormone), which includes CJC-1295. It binds to the GHRH receptor on the pituitary somatotrophs and enhances the amplitude of the natural secretion pulse. The modified version of CJC-1295 with DAC (Drug Affinity Complex) technology binds to plasma albumin, which extends the half-life period from minutes to several days. The version without DAC (often referred to as modified GRF 1-29) acts briefly and better preserves the pulsating nature of secretion.
The second class is GHRP (Growth Hormone Releasing Peptides) and selective agonists of the ghrelin receptor. These include Ipamorelin, GHRP-6 and GHRP-2. They act through the growth hormone secretagogue receptor (GHS-R), mimicking ghrelin. Ipamorelin is considered the most selective: it hardly increases cortisol and prolactin. GHRP-6, on the contrary, significantly stimulates appetite through the ghrelin pathway, which can be useful in the mass gain phase, but undesirable during drying.
The key advantage of this approach in theory is the preservation of the physiological feedback loop. Since the pituitary gland releases GH in pulses, and somatostatin limits excess, the risk of uncontrolled increase in GH level is lower than with injections of synthetic growth hormone. However, the long-term safety of these peptides in humans has not been systematically studied, and they are banned in sports by the World Anti-Doping Agency (WADA) in category S2.
Peptides that accelerate recovery and regeneration
Recovery of connective tissue is one of the most discussed areas of peptide application among strength athletes. Two compounds dominate this niche: BPC157 and TB500. Both have shown interesting results in clinical trials.
BPC-157 (Body Protection Compound-157) is a synthetic peptide of 15 amino acids (sequence Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val, molecular weight about 1419 Da), derived from gastric juice protein. In rat models, BPC-157 accelerated tendon healing by 60–80% compared to control and reduced gastric ulcer area. Presumed mechanisms include stimulation of angiogenesis (formation of new vessels) through the VEGFR2 pathway and modulation of nitric oxide.
TB-500 is a synthetic fragment of 17 amino acids, corresponding to the active part of the natural protein Thymosin beta-4 (43 amino acids, MW about 4963 Da). Thymosin beta-4 is present in almost all cells of the body, except erythrocytes, and is involved in actin binding, cell migration, and tissue repair. It is the actin-binding activity that underlies the hypothesis that TB-500 promotes muscle and ligament healing.
In practice, athletes often combine these two peptides, hoping for synergy: BPC-157 for local repair and anti-inflammatory action, TB-500 for systemic cell migration.
Peptides for fat burning
The idea of a "fat-burning peptide" is attractive, but it is especially important here to separate hope from evidence. The most famous compound of this group is AOD-9604 (Anti-Obesity Drug 9604), a fragment of the C-terminal part of the growth hormone molecule (amino acids 176–191). Theoretically, it should reproduce the lipolytic (fat-mobilizing) activity of GH without its effect on tissue growth and glucose levels.
It is also important to distinguish these compounds and approved drugs. The real scientifically confirmed progress in weight loss pharmacology is associated with GLP-1 receptor agonists - semaglutide and tirzepatide. In the STEP and SURMOUNT clinical trials, semaglutide provided a weight loss of an average of 15–17%, and tirzepatide - 20–22%.
GH secretagogues indirectly affect body composition: increasing endogenous growth hormone enhances lipolysis and may improve the ratio of muscle to fat mass. But the effect is moderate, develops slowly and largely depends on calorie deficit and training. No peptide replaces the basic principles: control of nutrition, strength training, and sleep remain the foundation of any body recomposition.