At a Pilates class, someone reportedly arrived with a paper lunch bag full of syringes.

The syringes contained peptides, an NPR producer recounted on the network’s Short Wave podcast. Similar products have moved from laboratory catalogs into gyms, wellness clinics and social-media feeds, where influencers promote them as shortcuts to faster recovery, more muscle and a younger body.

Fitness TikToker Noah Jay, for example, told followers that the peptide BPC-157 had healed his shoulder injury. “I absolutely love this stuff!” he said in a video. Of course, his profile also linked to a retailer discount code.

The peptide craze rests on a scientific half-truth. Peptides are real biological molecules, and some have transformed medicine. For instance, insulin is a peptide. So is oxytocin, more famously known as the “love hormone.” The active ingredients in several widely used obesity and diabetes drugs also belong to this broad family.

But that does not mean that every vial labeled “peptide” is an effective medicine — or even safe to inject.

Many of the compounds promoted online have never passed through the clinical trials required to establish a drug’s dose, benefits and risks. Some have barely been tested in humans at all. Buyers may also receive products labeled “for research use only,” a phrase that signals they were never manufactured as medicines for people.

The result is a market in which sophisticated-sounding molecules have become available far faster than scientists can determine what they actually do.

A Real Field of Medicine Meets Internet Biohacking

A peptide is a short chain of amino acids, the same building blocks that form larger proteins. The human body produces millions of them, using them to carry messages, control hormones, regulate inflammation and coordinate cell growth.

Their flexibility makes peptides attractive drug candidates. Researchers can design them to fit biological targets with considerable precision, and pharmaceutical companies have developed peptide medicines for diabetes, cancer, osteoporosis and other conditions. A recent review of peptide and related drug approvals described a field expanding through new techniques that make the molecules more stable and easier to deliver.

These successes lend an aura of credibility to the broader peptide market. Yet the difference between an approved peptide drug and a vial purchased through an influencer is vast. An approved medicine has gone through controlled studies, manufacturing checks and regulatory review. An experimental peptide sold online may have none of those safeguards.

For instance, let’s come back to BPC-157. Online sellers and wellness clinics promote it for tendon injuries, digestive problems, inflammation and muscle recovery. Researchers originally derived the compound from a fragment of a protective protein found in gastric juice.

Animal experiments have produced intriguing findings. In rodents, BPC-157 has appeared to influence inflammation, blood-vessel formation and tissue repair. But promising results in rats do not reliably predict what will happen in people.

“We might predict, you know, substance XYZ is going to be really safe and be totally wrong,” Paul Knoepfler, a cell and molecular biologist at the University of California, Davis, told NPR’s Short Wave. “Like, it might be fine in rats and mice, but it’s toxic in people.”

A 2025 review of BPC-157 for musculoskeletal healing found an extensive animal literature but little clinical evidence supporting its use in people. A more recent scientific assessment counted fewer than 30 participants across three published human studies, none of which was a randomized controlled trial.

Healing Signals Can Also Carry Risks

One proposed benefit of BPC-157 involves angiogenesis, the process through which the body grows new blood vessels.

New vessels can help damaged tissue obtain oxygen and nutrients. In principle, that could aid the repair of an injured tendon or ligament. But the same process can also supply blood to abnormal cells.

“Probably most of us are walking around with cells that are partway down the road to becoming cancerous,” Knoepfler told NPR’s podcast. “And so that’s one of my worries with these peptides, is that they’ll kind of encourage moving along the pathway towards an actual cancer.”

The larger problem is that researchers lack the human data needed to measure either the risk or the claimed benefit.

“You must test these in clinical trials to be sure of anything positive or negative,” Knoepfler told NPR.

Dose adds another layer of uncertainty. A substance can help at one concentration, do nothing at another and cause harm at a higher one. Yet online peptide users often assemble “stacks” of several compounds and follow dosing schedules shared by influencers, clinic owners or anonymous forum members.

“You can’t just make up what dose to take,” Knoepfler told NPR. “There’s often no apparent rhyme or reason to the wellness peptide doses people are taking.”

Quality Control is Important

Even the contents of the vial may be uncertain. Research-grade products do not have to meet the manufacturing standards applied to approved injectable medicines. A product may contain too much or too little of the advertised peptide, degradation products left over from manufacturing, bacteria or other contaminants.

The Food and Drug Administration has specifically raised concerns about BPC-157 impurities and the possibility that the molecule could trigger an immune reaction. The agency says it has only limited safety information for the proposed methods of administration and cannot determine whether the compound would harm humans. Other peptides promoted online, including CJC-1295, ipamorelin, KPV and TB-500, appear on the FDA’s list of substances with potential significant safety risks.

CJC-1295 has been associated with increased heart rate and a reaction involving widened blood vessels, according to the agency. For KPV and TB-500, the FDA says it has not identified adequate human exposure data for the promoted uses.

Absence of evidence does not prove that these drugs are dangerous. But it also does not make them safe.

What Compounding Can and Cannot Prove

Some patients obtain peptides through doctors rather than internet retailers.

Dr. Amanda Kahn, who runs a concierge practice in Manhattan, says that patients often visit her after seeking help for chronic pain or inflammation elsewhere. She sometimes prescribes experimental peptides as an additional treatment, while making their uncertainty clear.

“I don’t overpromise that this is a cure-all,” Kahn told NPR.

Doctors who prescribe such products may send orders to compounding pharmacies, which prepare customized medications for individual patients. Compounding serves a legitimate role in medicine. A pharmacist might remove an ingredient that causes an allergy, turn a pill into a liquid for a child or produce a dosage that is not commercially available.

But a compounded drug is not an FDA-approved drug. The agency does not evaluate every compounded product for safety, effectiveness or manufacturing quality before it reaches patients. Its guidance on compounded-drug risks warns that contamination or incorrect concentrations can cause serious injury or death.

Oversight also depends on where the product is made. State pharmacy boards supervise many traditional compounding pharmacies, while FDA-registered outsourcing facilities face additional federal requirements. Pharmacies operating under Section 503A of federal law do not follow all the manufacturing rules imposed on conventional drug companies.

Scott Brunner, chief executive of the Alliance for Pharmacy Compounding, argues that this system can still offer a safer route than the online gray market.

“The oversight is rigorous and appropriate for a pharmacy making one drug for one patient” under a doctor’s prescription, Brunner told NPR.

The FDA Confronts a Market That Already Exists

On July 23 and 24, 2026, an FDA advisory committee will begin examining whether seven peptide compounds should become eligible for pharmacy compounding.

The FDA meeting agenda includes BPC-157, KPV, TB-500, MOTs-C, emideltide, Semax and Epitalon. The proposed uses range from wound healing and obesity to insomnia, migraines and opioid withdrawal.

FDA scientists recommended against adding all seven to the compounding list, citing inadequate human trials and unresolved questions about contamination, immune reactions and dosing. The advisory committee’s votes are not binding; the agency will make the final regulatory decisions.

The debate has exposed an uncomfortable problem. Restricting peptides may push determined users toward overseas vendors and mislabeled research chemicals. Permitting compounding could improve manufacturing and medical supervision, but it might also give experimental treatments a legitimacy that the evidence does not support.

“We are talking about peptide drugs that you would only be able to get with a prescription from a licensed, legitimate provider,” Brunner told NPR’s podcast. “And it would be filled by legitimate state-licensed pharmacies.”

Howard Sklamberg, a former FDA deputy commissioner, rejected the broadest version of that harm-reduction argument.

“If you accept that argument in its extreme version, you just basically have to wave your hand at anything that’s — anything that ends up being popular,” Sklamberg told NPR.

Neither approach resolves the deeper problem: People are already injecting drugs that scientists have not adequately studied.

For now, consulting a physician and using a licensed pharmacy can reduce some risks, particularly the danger of contamination or receiving the wrong substance. But even so, don’t expect miracles. Nor can a doctor know the ideal dose of a compound when reliable dose-finding studies do not exist.

The peptide boom may eventually yield useful treatments. Modern medicine already shows how powerful these small molecules can become when researchers test them carefully.