Peptides are buzzy in longevity and biohacking circles. Neuroscientist and podcaster Andrew Huberman has described them as a “new kind of wedge in between supplements and prescription pills.” GQ called them “the hottest thing on the fringes of fitness and anti-aging.”Many are looking to peptides, a confusingly wide-ranging group of compounds, for a fitness and longevity edge.
But certain peptides are seemingly better at building muscle than others. BPC-157, ipamorelin, and sermorelin, to name a few, are purported to affect growth hormone release, promote muscle growth, and cut fat. “The scientific basis for peptides in promoting muscle growth lies in their ability to directly affect muscle at the molecular level, often targeting receptors on cells or increasing hormonal levels,” says Major Brandon Roberts, Ph.D., C.S.C.S.
But as is usually the case, there is no magic pill for reaching your fitness goals: In isolation without diet and intensive exercise, the data suggest limited efficacy. Experts warn taking off-label peptides for muscle growth comes with significant potential health risks.
Susie Reiner, Ph.D., is an exercise physiologist and founder of TheoryEx Performance, a scientific consulting agency. She is also the Head of Science at Aletha Health.
Nick Barringer, Ph.D., R.D.N., is a nutritional physiologist, registered dietitian, and certified strength and conditioning coach. He currently serves as the Chief Academic Officer and Dean of Graduate Studies at Lionel University.
Michael Genovese, M.D., is a board-certified physician and the Chief Medical Advisor at Ascendant New York.
Shelley Balls, M.D.A., R.D.N., L.D.N., is a registered dietitian at Consumer Health Digest and the owner of Fueling Your Lifestyle, a private-practice nutrition service.
Major Brandon Roberts, Ph.D., is a certified strength and conditioning coach and tactical strength and conditioning specialist. He is a research physiologist at the U.S. Army Research Institute of Environmental Medicine.
Peptides are short chains of amino acids, the building blocks of proteins. While that may seem straightforward, peptides encompass thousands of compounds with vastly different functions.
Vasopressin, for instance, is an anti-diuretic peptide. And glucagon-like peptide 1 (GLP-1) is famed for its ability to regulate blood sugar and appetite, mimicked by GLP-1 receptor agonist drugs like Ozempic and Wegovy.
A particular class of peptides, called growth hormone secretagogues (GHS), specialize in muscle growth and fat loss. GHS peptides, including sermorelin and ipamorelin, boost the release of human growth hormone (hGH) and insulin-like growth factor 1 (IGF-1)—which stimulate muscle growth and fat loss, and improve exercise performance and muscle recovery.
For this reason, GHS peptides are a popular hGH alternative among bodybuilders. Cell, animal, and early human studies hint at the potential for peptide use in sport. However, whether GHS peptides actually improve body composition, exercise performance, or recovery isn’t clear. Scientists also don’t know how GHS peptides affect different muscle groups, or what kinds of fitness goals they’re most effective for.
Research is still lacking when it comes to specific peptides, their uses, and long-term safety, says exercise physiologist Susie Reiner, Ph.D.. “There are currently no GHS peptides with FDA approval for promoting muscle growth in healthy populations, so none have been robustly proven to be effective,” adds tactical strength and conditioning specialist Major Brandon Roberts, Ph.D.. They suggest steering clear of non-prescription use.
Although the jury is still out on peptides for muscle growth, there are a few peptides that show promise. “These peptides might enhance the body’s natural anabolic pathways, leading to increased muscle mass and strength,” says Roberts.
Sermorelin, the synthetic version of naturally occurring growth hormone-releasing hormone (GHRH), has been gaining some attention as an alternative to weight loss injectables like Mounjaro and Wegovy. Proponents claim the synthetic peptide may help you shed pounds and build muscle simultaneously.
GHRH is produced by the hypothalamus and triggers the pituitary gland to produce hGH (or growth hormone), which triggers the production of IGF-1 in the liver. IGF-1 helps to regulate muscle protein synthesis (MPS)—the process of repairing muscle tissue damaged during exercise—which can help increase muscle growth and strength.
In short: “Sermorelin has been shown to increase hGH and IGF-1 levels, thereby promoting muscle growth,” says Reiner.
While it’s not approved for the purpose of building muscle in healthy individuals, it can be prescribed by a doctor for individuals who are deficient in hGH.
Ipamorelin is another growth hormone-releasing peptide (GHRP). It’s commonly used to stimulate muscle growth and improve post-workout recovery and metabolism.
In the body, ipamorelin mimics ghrelin, a hormone that stimulates hunger, helps prevent muscle wasting, and regulates fat storage. As the ghrelin receptor also regulates growth hormone release, it can boost muscle growth.
The FDA banned compounding pharmacies from selling ipamorelin and others in 2023 due to reported adverse events, including death; however, in September 2024, after further investigation, ipamorelin was removed from this list.
CJC-1295 seems like an all-around longevity-supporting peptide, with increased muscle mass and weight loss at the top of the list. It’s often used in combination with ipamorelin or other GHS agents for compounded anti-aging and muscle growth benefits.
This synthetically manufactured peptide mimics growth hormone-releasing hormone (GHRH), stimulating the release of hGH, which effectively promotes muscle growth.
CJC-1295 was also banned by the FDA in 2024 because it carries a risk of increased heart rate and cardiac events. Compounded CJC-1295 also runs the risk of peptide impurities and harmful immune responses, according to the FDA.
BPC-157, known by biohackers as the “magic peptide,” is a fan favorite for its potential to boost gym gains, brain function, and more. Still, there’s a severe lack of peer-reviewed, scientific literature about BPC-157. What little evidence is available suggests it may be beneficial in tissue-healing processes, which is why athletes may turn to it for muscle recovery purposes.
The peptide, made from human gastric juice, is not approved for clinical use in any country. The FDA says there is “no legal basis for selling the compound as a drug, supplement, or food (though there is evidence for its illicit sale and use)”. Early, small-scale trials suggest potential efficacy in inflammatory conditions like interstitial cystitis and osteoarthritis. These trials are of low quality, and as such, use in widespread clinical practice is premature.
According to Roberts, there are currently no human studies specifically focused on the efficacy of IGF-1 LR3 for muscle growth. Despite its popularity in bodybuilding circles, most of the evidence for IGF-1 LR3’s anabolic effects stems from preclinical studies in cell and animal models, Roberts says. In these studies, it has been shown to promote satellite cell activation, enhance protein synthesis, and reduce muscle protein breakdown. In theory, these are all positive things if muscle growth is the desired outcome, but it is unproven.
IGF-1 is the downstream protein that mediates the effects of growth hormone. Due to a few modifications to the IGF-1 structure, IGF-1 LR3 has increased potency and longer circulating time. While this should logically increase the muscle-building effects, IGF-1 LR3 would also then bypass the internal feedback regulatory pathways, theoretically increasing the risk of negative side effects of excessive growth hormone pathway activity.
Ibutamoren, often called MK-677, like ipamorelin is a selective growth hormone secretagogue receptor (GHSR) agonist, meaning it stimulates the release of the muscle and bone-supporting growth hormone that your body naturally makes while also having appetite-stimulating properties.
Some studies have shown that ibutamoren increases fat-free mass. For instance, a 12-month randomized controlled trial involving older adults (ages 60 to 81) demonstrated a 1.1-kilogram increase in fat-free mass with ibutamoren compared to placebo. Additionally, ibutamoren supports GH pulsatility, an essential physiological characteristic for effective muscle and metabolic regulation. Though those results are interesting, Roberts points out limitations of the study: Participants’ thigh muscle cross-sectional area did not increase, indicating no improvement in muscle size; and muscle strength, function, and quality of life did not improve, “so the fat-free mass gains should be interpreted with caution,” he says. Despite some promising data, ibutamoren was banned for use in compounding pharmacies by the FDA during the 2023 episode, but unlike ipamorelin and others, it currently remains banned due to concerns for heart failure.
Studies in patients with HIV using tesamorelin have shown that this peptide increases lean tissue mass while reducing fat accumulation, particularly in abdominal regions, says Roberts. This dual effect makes it a promising candidate for muscle growth and metabolic improvement, especially in populations with lipodystrophy (a group of disorders that affect how the body stores fat) or sarcopenia (age-related muscle loss).
Peptides, particularly GHS peptides, can be useful for treating growth hormone deficiency, says Roberts. Sermorelin is FDA-approved to treat growth hormone deficiency in children. Other peptides, like semaglutide, tirzepatide, and liraglutide, are proven treatments for obesity.
In adults, approved indications for growth hormone therapy include childhood-onset growth hormone deficiency, adult-onset hypopituitarism (underactive pituitary gland) due to pituitary or hypothalamic disease, AIDS-related wasting syndrome, and short bowel syndrome.
While peptides certainly have their benefits for specific populations, the benefits are overstated for healthy individuals using peptides off-label, says board-certified physician Michael Genovese, M.D.. And while anecdotal evidence may suggest benefits, the scientific data is less clear. “Without a clinical deficiency, the benefits don’t justify the risks for most people,” he says.
Peptide-based therapies for muscle growth, while promising in certain contexts including cell and animal studies, carry a range of risks and potential side effects, particularly when considering long-term health.
One of the primary concerns, according to Roberts, involves metabolic disturbances. GHS can mildly increase insulin resistance and glycated hemoglobin (HbA1c) levels over time. “Although these changes are generally not clinically significant in healthy individuals, they could pose a greater risk in populations predisposed to metabolic disorders, such as prediabetes or type 2 diabetes. These metabolic effects highlight the need for careful monitoring during prolonged use,” he explains.
Additionally, systemic side effects associated with sustained growth hormone stimulation include symptoms such as abnormal tissue growth, joint discomfort, and potential enlargement of the heart (cardiomegaly), Roberts says.
Elevated levels of insulin-like growth factor-1 (IGF-1), which is the downstream effect of GH activity, hav
