Peptides seem to be everywhere — and there are more on the way. Adherents promise these tiny chains of amino acids can help you lose weight, keep your skin clear, and slow down the aging process. While a person who really wants to acquire peptides right now can do so fairly easily, they are not, strictly speaking, legal — which might be why a peptide “club” with a 300-person waitlist has popped up in San Francisco.

But access could soon expand: Peptides have support from the nation’s wellness influencer-in-chief, US Health Secretary Robert F. Kennedy Jr., and the Food and Drug Administration is expected to relax restrictions for a dozen peptides.

“Peptide” is maybe the buzziest word in health care right now — but, as usual, the social media mania masks a much more complicated scientific reality. Peptides are not inherently bad, but not all of the peptides being hawked by wellness influencers are the same. Here’s what you should know.

To be clear, you have peptides in your body right now: Peptides are naturally occurring groups of amino acids that regulate a variety of physiological processes. There is nothing inherently strange or shady about a “peptide.”

“They help our body work,” Dr. Daniel Drucker, an endocrinologist at the University of Toronto who conducted some of the basic peptide research that helped lead to the development of GLP-1 drugs, told me. “They help us digest our food and absorb our nutrients. They send information to various organs to tell it how to utilize energy. They’re important for control of our heart and our blood vessels and our blood pressure and how our brain functions.”

And human beings have been harnessing the awesome power of peptides to protect themselves against illness for decades. Insulin itself, the diabetic treatment, is a peptide that is produced by the pancreas; back in the 1920s, two scientists removed insulin from a dying dog’s pancreas, injected it into a diabetic dog, and kept the latter alive for more than two months. With that, diabetes was no longer a death sentence for people, but a treatable condition. Scientists later learned to develop synthetic peptides; the insulin that people take today doesn’t come from dogs, it’s the result of a complex manufacturing process.

Once we had harnessed the power of the peptide, it led to more breakthroughs. And a century later, another peptide-based diabetes treatment is leading a new medical revolution.

Semaglutide — the active ingredient in Ozempic and Wegovy — is a synthetic peptide that was initially developed to help people with diabetes produce insulin. It mimics the function of GLP-1, a naturally occurring hormone that regulates people’s insulin production and slows down their digestion.

But that success has opened the door for unscrupulous actors to take advantage of the hype.

The problem starts with the GLP-1 treatments. In late 2022, just as Ozempic and Wegovy were starting to see more widespread usage for weight loss, there was a shortage that would last for all of 2023, 2024, and into 2025. People still wanted to lose weight, though, so they sought out alternative GLP-1s on the black or gray markets. Because these drugs use naturally occurring peptides, compounding pharmacies — businesses that create custom-made medications — are able to produce their own bootleg versions. The GLP-1 peptides produced by major pharmaceutical companies have been subjected to years of clinical and safety testing, and their manufacturing is subject to FDA oversight. That isn’t true for the peptides, GLP-1 or otherwise, that are produced by compounding pharmacies.

Still, many patients flocked to these, despite the safety concerns and warnings from regulators about the risks.

Even though the sanctioned drug supply has recovered, the GLP-1 peptide market is robust, and often drafts off legitimate drug development breakthroughs. Right now, you can find doctors on TikTok pitching knockoff versions of a new weight-loss medication that’s shown promising results in clinical trials but is not yet approved by the FDA.

Dr. Eric Verdin, president and CEO of the Buck Institute for Research on Aging, pointed out to me that if you look closely at the bottles for these products, they frequently feature words that should be taken as a warning: “Not FDA approved. For research purposes only.”

“So if you decide to inject this, you have the right to do it from my standpoint, but good luck with it,” he said. “Not tested, not proven, not certified in terms of sterility and so on.”

What experts really worry about is that the success of some legitimate peptides have effectively served as a gateway drug to a whole new range of “treatments” with not only purity concerns, but flimsy evidence of their clinical value.

As compounding pharmacies attracted new customers during the GLP-1 shortage, they also seized the opportunity to push a range of other peptide treatments. Today, there is a whole universe of acronyms and scientific-sounding names that influencers and even some doctors are promoting as a new generation of treatments: BPC-157, TB-500, CJC-1295, and ipamorelin.

Some of these products have actually been around for years. Dr. Spencer Nadolsky, a weight-loss specialist, told me that he had actually tried BPC-157 a decade ago to help with injuries he was dealing with. (“It didn’t help me,” he said.) But they began seeing new interest after the public became familiar with peptides through GLP-1s.

There’s one big problem: Many of these other peptides have extremely limited or nonexistent evidence for their effectiveness in human beings — despite what you may hear on an Instagram reel or a TikTok video.

Proponents of peptides will sometimes point to preliminary or preclinical evidence of their benefits. Sounds good, right? But that evidence is often limited to animal (typically mouse or rat) trials.

There are several important reasons to be skeptical that a successful result in a mouse will be replicated in humans. To state the obvious, mice and people have different physiologies. The rodents also tend to be alike in age and health, and they’re being tested under optimal clinical circumstances. By one recent estimate, although 50 percent of the drugs tested in animals do go on to be tested in humans, only 5 percent are ultimately approved for use by people.

“Just because the mouse or rat did not die in the experiments that were done, you can’t assume that a human will not get sick and get into trouble,” Drucker said.

That is why FDA-approved medications go through years of safety and efficacy testing. By taking an unapproved peptide, you’re putting something in your body that skipped almost all of the rigorous, difficult drug development process, which many promising potential treatments fail for one reason or another.

Once the normal drug development process is over, people can have faith that they know what they’re putting in their body. You have no such guarantees taking off-market peptides.

“We really don’t know the extent of what it’s doing. We don’t know. We don’t know what dose to use,” Dr. Nir Barzilai, director of the Einstein Institute for Aging Research at Albert Einstein College of Medicine, told me. “It’s crazy. It’s really another snake oil.”

The experts I spoke with worry that people will have to learn that lesson the hard way. They are expecting more stories like the two people who became seriously ill after being injected with peptides at a Las Vegas longevity convention by someone who did not have permission to practice medicine or dispense prescriptions in Nevada. In our new DIY era of health and wellness, that seems to be the only way some people learn. (See: the former anti-vaxxers who are turning to measles shots as the disease takes root in communities across the US.) If you are going to insist on taking a peptide, Barzilai said you should consider getting it tested by one of the lab companies that have popped up amid the peptide craze. That way, you can make sure it is what you think it is.

Americans’ cavalier attitude toward health and wellness and what we put in our bodies will come at a cost, the experts told me. As peptide use grows, it becomes more likely something will go wrong.

“There’s going to be a backlash,” Verdin said. “Unfortunately, that often seems like the only way we can learn collectively is for something tragic to happen. Then we kind of have a wake-up call and get back to a little more reasonable place.”