Sarah Keese knew within seconds after injecting the peptide sermorelin into her stomach that something was wrong. Flushed and lightheaded, she cried out to her boyfriend for help. As Keese walked toward him, she fell to the ground, unconscious.

The next thing Keese remembers is being carried into the emergency room at the hospital in Sheridan, Montana. She later learned that her heart rate had slowed to 20 beats per minute, her blood pressure had crashed, and she had stopped breathing briefly after suffering a severe allergic reaction to the gray-market peptide. “If I had not been in the ER, I would have died absolutely,” says Keese, 35, an engineer now based in Anchorage, Alaska.

Keese was given epinephrine, then flown by medical helicopter to a larger hospital in Missoula, Montana, for more treatment and observation on July 3, 2025. That landed her with an $80,000 medical bill and a series of follow-up visits to a cardiologist to check on an irregular heartbeat triggered by the anaphylactic shock. She’s now sworn off peptides.

Sermorelin was approved for sale by the FDA in 1997 to treat children with slow physical development. It stimulates the pituitary gland to produce human growth hormone. Sold under the name Geref, the drug was discontinued by its creator EMD Serono in 2008 for commercial reasons. Now, sermorelin and a group of similar peptides have seen a surge in popularity among fitness fans, who claim their ability to stimulate the body’s natural growth hormone can supercharge building muscle, shredding fat and speeding injury recovery.

But the family of peptides that sermorelin belongs to, known as “secretagogues,” poses a risk of triggering allergic reactions. Forbes interviewed five people, including Keese, who experienced such reactions after taking secretagogues. Dozens of others have shared similar accounts on social media. Without testing what Keese and the other peptide users took, it’s impossible to know whether their reactions were a side effect of the drug, or caused by other ingredients or contaminants.

Peptides are a large category of amino acid-based drugs that include legal ones, like GLP-1 weight-loss medications and insulin. More and more people are experimenting with loosely regulated peptides like secretagogues, which have become a hit among workout enthusiasts looking for an edge to train harder and look better. But there’s little scientific data on their safety or efficacy, and the FDA has not approved them for weight loss or workout recovery.

These drugs are now readily available on the internet from sketchy sellers who hawk them with little oversight. In this shadowy online bazaar, which could be worth as much as $4 billion, peddlers exploit a loophole in the law under which peptides can be sold for “research purposes.”

“The safety and efficacy are unknown, so why would you want to be putting something like that in your body?”Dr. Thomas Kremen, a sports medicine doctor at UCLA Health

Jack Ryan, 19, who publishes research about peptides on his site PeptidePrices, says that he now tracks nearly 1,000 online storefronts. As of September 20, 526 of them were selling sermorelin and 714 were selling tesamorelin, a related peptide that has also caused allergic reactions. (PeptidePrices also accepts affiliate links from sellers.)

Purchasing online peptides is a dice roll. Fitness enthusiasts who buy gray-market drugs........

© Forbes