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MIT Technology Review Explains: Let our writers untangle the complex, messy world of technology to help you understand what’s coming next. You can read more from the series here.

Want to lose weight? Get shredded? Stay mentally sharp? A wellness influencer might tell you to take peptides, the latest cure-all in the alternative medicine arsenal. People inject them. They snort them. They combine them into concoctions with superhero names, like the Wolverine stack.  

Matt Kaeberlein, a longevity researcher, first started hearing about peptides a few years ago. “At that point it was mostly functional medicine doctors that were using peptides,” he says, referring to physicians who embrace alternative medicine and supplements. “In the last six months, it’s kind of gone crazy.”

Peptides have gone mainstream. At the health-technology startup Superpower in Los Angeles, employees can get free peptide shots on Fridays. At a health food store in Phoenix, a sidewalk sign reads, “We have peptides!” At a tae kwon do center in South Carolina, a peptide wholesaler hosts an informational evening. On social media, they’re everywhere. And that popularity seems poised to grow; Department of Health and Human Services secretary Robert F. Kennedy Jr. has promised to end the FDA’s “aggressive suppression” of peptides.

The benefits and risks of many of these compounds, however, are largely unknown. Some of the most popular peptides have never been tested in human trials. They are sold for research purposes, not human consumption. Some are illegal knockoffs of wildly successful weight-loss medicines. The vast majority come from China, a fact that has some legislators worried. Last week, Senator Tom Cotton urged the head of the FDA to crack down on illegal shipments of peptides from China. In the absence of regulatory oversight, some people are sending the compounds they purchase off for independent testing just to ensure that the product is legit. 

What is a peptide?

A peptide is simply a short string of amino acids, the building blocks of proteins. “Scientists generally think of peptides as very small protein fragments, but we don’t really have a precise cutoff between a peptide and a protein,” says Paul Knoepfler, a stem-cell researcher at the University of California, Davis. Insulin is a peptide, as is human growth hormone. So are some neurotransmitters, like oxytocin. 

But when wellness influencers talk about peptides, they’re often referring to particular compounds—formulated as injections, pills, or nasal sprays—that have become trendy lately. 

Some of these peptides are FDA-approved prescription medications. GLP-1 medicines, for example, are approved to treat diabetes and obesity but are also easily accessible online to almost anyone who wants to use them. Many sites sell microdoses of GLP-1s with claims that they can “support longevity,” reduce cognitive decline, or curb inflammation. 

Many more peptides are experimental. “The majority fall into the unapproved bucket,” says Kaeberlein, who is chief executive officer of Optispan, a Seattle-based health-care technology company focused on longevity. That bucket includes drugs that promote the release of growth hormones, like TB-500, CJC-1295, and ipamorelin, and compounds said to promote tissue repair and wound healing, like BPC-157 and GHK-Cu. It’s primarily these unapproved compounds that have raised concerns. “Anybody can set up an online shop selling research-grade peptides,” says Tenille Davis, a pharmacist and chief advocacy officer at the Alliance for Pharmacy Compounding, a trade organization representing more than 600 pharmacies. “And nobody knows what’s even in the vials.”  

It’s not just fitness gurus, biohackers, and longevity fanatics who are taking these experimental drugs. Kaeberlein recalls hearing about an acquaintance whose doctor prescribed her unapproved peptides. She was “just a typical upper-middle-class woman,” he says. “That’s when it really hit me that this has sort of gone relatively mainstream.”

What do peptides do?

All kinds of things, purportedly. GHK-Cu is supposed to help with wound healing and collagen production. BPC-157 is said to promote tissue repair and curb inflammation, TB-500 to foster blood vessel formation. Here’s the caveat: The evidence for these benefits comes largely from animal studies and online testimonials, not human trials. “There’s no human clinical evidence to show that they even do what people are claiming that they do,” says Stuart Phillips, a muscle physiologist at McMaster University in Hamilton, Ontario. “So it could be just a giant rip-off.”

Some experimental peptides probably do have beneficial wound healing properties or regenerative effects, Kaeberlein says. For BPC-157, for example, “the animal data is compelling,” he says. But there are still plenty of unknowns: What is the right dosage? How long should you take it? What’s the best way to administer it? Those are questions that can be answered only through rigorous clinical trials. In the absence of those studies, doctors “just make up their own protocols,” he says. Some consumers go the DIY route, reconstituting powdered peptides and injecting their own concoctions at home. 

So why am I seeing ads for these peptide therapies if they’re not approved? 

Federal law prohibits companies from marketing medications that haven’t been approved. That includes most peptides, which are regulated as small molecules, not dietary supplements. (Two notable exceptions are collagen peptides and creatine peptides, often sold as powders.) The law is designed to protect consumers from drugs that haven’t been proved safe and effective.

But it doesn’t stop labs from making peptides for research purposes. “Most of the peptides being consumed in the marketplace now are being sold by these online companies that are selling them labeled for research use only,” Davis says. The vials often bear disclaimers that clearly say as much: “For research use only” or “Not for human consumption.” It’s illegal to market these products for human use, but “the websites make it pretty clear that the buyers are intended to be using these products themselves,” she says.

The practice isn’t legal, but enforcement has been sporadic. “FDA sends warning letters, shuts down companies. But because it’s all online, they have a really hard time keeping up with these entities,” Davis says. And companies have plenty of incentive to keep illegally marketing the products. “They can make millions of dollars without having to spend money and time doing research,” Knoepfler says. “It’s a cash grab.”

Compounding pharmacies, which are legally allowed to create bespoke medications by mixing bulk active ingredients, often get requests to dispense peptides, but most peptides don’t meet the eligibility criteria for compounding. This has always been the case, but in 2023 the FDA explicitly added several common experimental peptides to the list of bulk substances that cannot be compounded because of safety concerns. “It put an exclamation point on policy that was already in place,” Davis says.  

Many GLP-1 medications are available from compounding pharmacies. That used to be accepted because the drugs were in short supply. Now, however, supplies of most of these medications are stable, and sellers are under increasing pressure from regulators to stop mass-marketing these drugs. 

What’s the harm in trying them? 

Peptides sold for research purposes come from labs with little regulatory oversight. “When you buy stuff online intended for research grade, you have no idea what’s in the vial that you’re getting. You have no idea the sterility practices that it was manufactured under, or what sort of impurities might be in the vial,” Davis says.

Phillips has heard some people say they send their peptides for third-party testing to ensure that they’re pure, “like it’s some kind of flex,” he says. “And I’m like, ‘Well, you just proved that this stuff lives in the shadows, for crying out loud.’”

Finnrick Analytics, a peptide-testing startup in Austin, Texas, has analyzed the purity and potency of more than 5,000 samples of 15 different peptides from 173 vendors. The results show that the quality varies substantially from vendor to vendor and even batch to batch. For example, the company tested nearly 450 samples of BPC-157 from 64 vendors. In some cases, the vials sold as BPC-157 didn’t contain the compound at all. In those that did, the purity varied from about 82% to 100%. 

Perhaps more worrying, 8% of all the peptide samples Finnrick tested had measurable levels of endotoxins, bacterial fragments that can cause fever and chills or, in larger doses, septic shock. 

The health risks aren’t just hypothetical. In 2025, two women had to be hospitalized and placed on ventilators after receiving peptide injections at a longevity conference in Las Vegas. Both recovered, and it’s still not clear whether they reacted to the peptides themselves or to some impurity in the vials. 

“The idea that all peptides are safe and all peptides are natural is just nonsense,” Kaeberlein says. “I tend to consider myself fairly libertarian when it comes to what people want to do for their health,” he adds. “If you want to take an experimental drug, that’s up to you.” But the problem with unregulated experimental therapies is that it’s exceedingly difficult to assess benefit and harm. “The relatively small percentage of people that are bad actors will be bad actors, and they will dishonestly market this stuff to people who aren’t equipped to really understand the true risks and rewards,” he says.

And, like any drug, peptides come with a risk of side effects. For approved medications, these are detailed right on the package insert. But for many experimental peptides, there hasn’t been enough research to understand what those side effects might be. Some researchers have warned that peptides that promote growth or blood vessel formation might also foster the growth of cancers.  

For competitive athletes who use peptides, meanwhile, the risks include not just possible health problems but suspension. Some peptides, like BPC-157, are banned by the World Anti-Doping Agency. 

The FDA has undergone a pretty substantial overhaul under the Trump administration. Are the regulations around peptides likely to change? 

I don’t have a crystal ball, but it seems likely. In May 2025, US health secretary Robert F. Kennedy Jr. joined the longevity enthusiast and biohacker Gary Brecka on his podcast The Ultimate Human and promised to “end the war at FDA against alternative medicine—the war on stem cells, the war on chelating drugs, the war on peptides.”

Knoepfler anticipates that Kennedy will force the FDA to allow compounding of some of the most popular peptides, like BPC-157 and GHK-Cu. “Such a step would put public health at great risk, while giving compounders and likely wellness influencers a lot more profit,” he says. 

The FDA seems intent on cracking down on GLP-1 copycats, however. In early February, commissioner Marty Makary posted on X that the agency would take “swift action against companies mass-marketing illegal copycat drugs, claiming they are similar to FDA-approved products.”