What are peptides, and are they safe?

You may have heard about peptides lately from a wellness influencer, your gym friend, or our secretary of Health and Human Services. 

The purported benefits of taking peptides are wide-ranging: more muscle, less fat, better memory, quicker wound healing and healthier skin. But what are they? And are they safe? Can they really do what their promoters claim?

Here’s what we know about peptides, and how the U.S. Food and Drug Administration might act to make them more accessible.

What are peptides?

Peptides are short chains of amino acids — basically fragments of proteins. They occur naturally in the body, and we also get them through the food we eat. 

They help digestion, trigger ovulation, regulate blood pressure, and more. Insulin, the hormone that helps the body process sugar in the blood, is a peptide. 

Like scientists have done with insulin, some peptides have been synthesized outside the body and turned into medications. 

There are several FDA-approved peptide medications with wide-ranging applications. Among them: increasing certain hormone production (tesamorelin), treating a light-exposure disorder (afamelanotide) and improving libido (bremelanotide). 

The latest class of diabetes and weight-loss drugs, GLP-1s such as Ozempic and Zepbound, are peptides.

Other peptides, like collagen peptides, can be taken orally and sold over the counter like other vitamins and dietary supplements. 

Non-FDA-approved peptides

FDA-approved peptide medications were approved to treat specific conditions, but physicians can prescribe them off-label to treat other conditions. Even if they are being used off-label, FDA-approved peptides have been tested for safety in clinical trials.

The same is not true for numerous non-FDA-approved peptides being used by athletes and people in the wellness space. A vast majority of these peptides are injected. 

These injectable peptides, many of which have Star Wars droid-like names, have a wide range of purported benefits.

CJC-1295 and Ipamorelin, for example, are said to improve muscle mass, cognition, and sleep by stimulating the production of human growth hormone. Peptides like BPC-157 and TB-500 are promoted for muscle and tissue healing. Some people recommend taking them together, a peptide cocktail they call the "Wolverine stack." There are even peptides like Melanotan that purport to improve tanning. These are just a few of the growing peptide options on the market — several of which are banned for professional athletes by the World Anti-Doping Agency. 

Most of the safety and efficacy evidence for these peptides comes from studies in animals — not humans. The lack of clinical data in humans can make it challenging to figure out proper dosing, and long-term safety risks are unknown. 

"Each of the ten or so most popular peptides remain somewhat of a mystery in terms of their impacts when used in people," said Paul Knoepfler, a cell and molecular biologist at the University of California Davis School of Medicine. 

Like GLP-1s, some of these medications may one day be approved therapeutics, but currently, evidence is limited. Doctors caution against using peptides without physician oversight. 

Current regulatory landscape

Before 2024, many pharmacists were permitted to compound peptides when prescribed by a doctor. But in late 2023, because of safety concerns, the FDA recategorized more than a dozen peptides, making them ineligible for compounding pharmacies to make them. 

A gray market emerged with online retailers marketing the peptides for their health benefits while also adding disclaimers that they should only be used as "research chemicals" or for "research use only" or not for human consumption. 

That hasn’t stopped online shoppers from buying and self-administering the medication. 

"No one really knows what dose to use, whether combining different peptides together adds more risks like toxicity, whether the peptides could increase cancer risk such as through stimulating new blood vessel growth, and the list goes on," Knoepfler said.

Beyond peptides’ unknown safety risks, getting injectable medications online comes with additional uncertainty. Finnrick, a Texas lab that provides free testing of online peptide retailers, has found that what is being advertised isn’t always what’s then sold to buyers.

Health and Human Services Secretary Robert. F. Kennedy Jr. rose to prominence as an attorney who questioned the safety of common childhood vaccines, calling for what he terms "gold-standard" placebo-controlled clinical trials.

When it comes to peptides, which he said he uses, Kennedy said he’s poised to make them more accessible. He promised to end the "war on peptides" and, in a Feb. 27 interview with podcaster Joe Rogan, said his agency would take action within weeks.

He did not mention that most peptides do not have the randomized placebo-controlled clinical trials that he demands of other pharmaceuticals.