What are peptides? Proponents claim the supplements can help boost athletic performance

Dr. Jesse Mills regularly sees men who want to improve something about their body.

Mills, the director of the Men’s Clinic at UCLA Health, usually offers advice like diet, exercise — maybe physical therapy to help recover from an injury.

In recent months, however, some patients have come to him with a solution already in mind: peptide therapy. 

“Week by week more people are asking about peptides,” Mills said.

Peptide therapy has become a mainstay online and in fitness communities. Popular figures including Andrew Huberman and Joe Rogan have discussed them on podcasts. On Reddit, one group focused on peptides has 100,000 subscribers, where users are flocking to them looking to tone their physique, recover faster from injuries, sleep better and even improve skin tone. In February, the telehealth giant Hims & Hers announced it had acquired a peptide facility in California to help “deliver personalized medications.” 

“Everybody’s looking for that edge and everybody’s looking to build the perfect Hollywood body,” Mills said. “I think the thought is that they look at it [peptide therapy] as a more natural way of doing either growth hormone replacement or testosterone replacement.”

However, while there are some small studies suggesting certain peptides may have benefits, there’s no strong evidence that peptide therapy provides any meaningful difference in performance and recovery, experts said. 

“You have to do your research to know what actually has undergone human trials and what has undergone podcast trials,” Mills said. 

What are peptides?

Peptides are short chains of amino acids, the building blocks of proteins. Long peptide chains will fold onto themselves and link with other peptide chains, forming proteins.  

A huge range of molecules found in the body are peptides, including insulin, oxytocin and endorphins. Many other synthetic peptides — made in a lab — are approved as drugs, including semaglutide (the active ingredient in Ozempic) and linaclotide (the active ingredient in Linzess, a drug for irritable bowel syndrome). 

But a number of peptides — not approved by the Food and Drug Administration and entirely unregulated — have grown in popularity, pitched as solutions to shorten recovery time from injuries, enhance athletic performance and improve libido. 

“The ones that are getting attention in the gym are what we call ‘secretagogues,’” Mills said, which are popular because of the belief they can aid in muscle growth and repair.

This includes a synthetic peptide called sermorelin. Sermorelin is meant to act on the pituitary gland in the brain, telling it to release human growth hormone, which, in turn, leads to higher levels of insulin-like growth factor-1, a molecule that’s believed to help stimulate muscle growth and repair. 

Dr. Larry Lipshultz, chief of the division of male reproductive medicine and surgery at the Baylor College of Medicine in Houston, said that his patients who take sermorelin primarily take it because they want to lose body fat and have a more defined physique. 

“People who take it claim they feel better, they sleep better, they wake up more refreshed,” Lipshultz said. “But a lot of the problem with your peptides is there’s very little scientific evaluation of what they do and of their side effects.”

Another peptide popular in the fitness community is body protection compound-157, or BPC-157, Mills said. In lab studies, it’s been shown to promote wound and tissue healing, leading some to call it the “wolverine peptide.” 

It’s thought to work by promoting activity of fibroblasts, said Dr. Travis Dekker, an orthopedic surgeon at the United States Air Force Academy in Monument, Colorado. These are cells that can help to restore connective tissue such as tendons and ligaments after an injury. It’s also believed to help with synthesizing proteins, which could help with recovery, he said. 

He added that BPC-157 is the peptide he gets the most questions about from patients. 

“Athletes ask me, ‘Hey, I injured my rotator cuff. Can I get this online and then therapeutically injected into my rotator cuff?’” Dekker said.

The demand — and lack of strong evidence supporting the peptide’s use — led him to write a letter to the editor in the Journal of Arthroscopic and Related Surgery calling for more research into these compounds.

BPC-157 and sermorelin are both banned by the World Anti-Doping Agency, and, as of 2024, BPC-157 was listed as a prohibited substance by the NCAA.

Do they work and are they safe?

“If you have a drug that is manufactured by a big-brand pharmaceutical company, they won’t even bring it to the public until the due diligence is done with efficacy and side effects,” Lipschultz said. Peptides, he added, “just come out from these peptide laboratories with little or no studies.”

Most of the studies on popular peptides have largely been conducted in animals and there isn’t much data in humans. 

However, a handful of human studies suggest that some peptides might be worth exploring further in larger, more rigorous studies. 

A small study of 16 patients found that an injection of BPC-157 directly into the knee may help alleviate knee pain. Another small study, with just 12 participants, found that the compound helped reduce symptoms in women with interstitial cystitis, a painful bladder condition, after traditional treatment stopped working. No adverse events were reported in either study, but the small number of participants makes it difficult to draw broader conclusions. 

Another peptide, kisspeptin, has shown promise in improving libido in both men and women in two small randomized trials in the United Kingdom. The peptide is naturally occurring in the body, but synthetic versions also exist.

Lipschultz said that if he has patients who are trying to lose weight or having trouble sleeping, he will sometimes prescribe peptides through a compounding pharmacy, but only in addition to regular FDA-approved treatments. 

“I don’t treat people just with peptides,” he said. 

The lack of rigorous human studies also means that data about side effects is missing as well as proper dosing regimens, Dekker said. 

“We don’t know the duration or concentration of the drug that needs to be delivered,” he said. “We don’t know the timing during the day or the timing of when it is administered in the setting of an injury.”

As a result, patients often try a variety of doses at various intervals with unclear benefits. 

“I think that there’s still a lot more to be learned when it comes to these peptides and figuring out exactly what they’re doing,” Dekker said.