By Rachel Tompa

Stacking, research-grade, Wolverine — Stanford Medicine experts break down what we need to know about peptides, the latest internet wellness trend

Here’s a situation scientist Katrin Svensson, PhD, never expected to find herself in: Molecules she discovered in the lab and tested (so far, only in mice) have shown up on internet-based company websites for anyone to purchase and use to inject themselves.

These molecules are naturally occurring peptides and they’re the latest wellness craze among certain sectors of the population.

But the craze is getting far ahead of the science in many ways, said Svensson, a Stanford Medicine associate professor of pathology. The peptides she’s discovered (including a new anti-obesity peptide, BRP) have not been tested in humans, a key first step between lab research, U.S. Food and Drug Administration approval and clinical use, let alone been manufactured in a regulated, safe process for humans. And while her discoveries aren’t yet the subject of viral social media reels, many other research-grade — i.e., not for-human-use-grade — peptides are.

In the name of looksmaxxing, muscle building, weight loss or just general wellness, many people trade tips and tricks on social media and inject themselves with unapproved peptides sourced from a variety of online companies through what is known as a gray market for peptides. Is this a good idea? Definitely not, said Svensson and Jonathan Long, PhD, an associate professor of pathology who also conducts peptide research.

“First of all, there could be all sorts of contaminants in that solution that you’re injecting into yourself. Second, there’s no data about whether these peptides actually do anything or their toxicity,” Long said. “You just don’t know what you’re putting in your body.”

Katrin Svensson

Katrin Svensson

With an FDA advisory panel recently voting to recommend loosening restrictions for compounding pharmacies on six peptides that are far from FDA approval, the picture is even murkier. Should the FDA take the panel’s recommendation, loosened restrictions would allow patients to get certain peptides from compounding pharmacies that haven’t been through rigorous clinical testing for safety and efficacy. Long and Svensson worry that members of the public will get the wrong idea about the safety of using these peptides.

But there’s good news for people who are interested in the potential of peptides but are not into injecting untested and unregulated compounds: Several peptide-based drugs are FDA-approved and many more are making their way through clinical testing. The success of FDA-approved GLP-1-based weight loss drugs, which are probably the most commonly known peptide medications, have opened a door to a burgeoning new therapeutic field.

We asked Long and Svensson to break down peptide science: what these molecules are, what they do in the body, and why they might fuel the next great frontier for new and better therapies — once they are fully tested, that is.

What, exactly, are peptides?

Peptides are molecules that our body uses to send signals from cell to cell and from tissue to tissue. They’re short strings of amino acids, the same building blocks that make up proteins. Peptides are generally shorter than proteins, ranging from just three amino acids long to around 100 on the longer side. Proteins tend to be a few hundred to over 1,000 amino acids long.

Most peptides are made of proteins — the body dices up proteins into smaller chunks that are peptides — though scientists have also found some peptides that are coded directly by genes, as proteins are. Scientists have cataloged around 7,000 peptides in the human body, but it’s possible there are many more as yet undiscovered.
They act as lightning-fast messengers in our bodies, conveying signals from one organ to another such as, “just ate pasta, blood sugar incoming,” “time to sleep,” or, “let’s kill this cancer cell.” For example, the GLP-1 peptide is produced in the gut when we eat a meal and travels to the brain and to the pancreas, telling these organs we’ve had enough to eat and to start releasing insulin into the bloodstream, respectively.

“Peptides can act very fast, and they can be very potent in changing our behavior,” Svensson said.

Which peptides are actually medicine?
While GLP1 medications get all the headlines today, the first peptide-based medicine, insulin, was developed more than 100 years ago. It was discovered and isolated from a dog’s pancreas in 1921. In 1982, it also became the first commercially available synthetically manufactured peptide.

Jonathan Long

Jonathan Long
Insulin is a peptide and a hormone and is released by the pancreas to regulate blood sugar, helping shuttle glucose from the blood into cells that convert it to energy. People with type 1 diabetes are prescribed insulin because their bodies can’t make it, or make very little of it. Some people with type 2 diabetes also need insulin to keep their blood sugar steady as their bodies no longer respond correctly to their naturally produced insulin. The discovery of injectable insulin was lifesaving for diabetic patients.
Since injectable insulin came on the scene, the FDA has approved about 100 different peptide therapeutics for conditions ranging from diabetes to multiple sclerosis to septic shock.

Because peptides are broken down by the digestive system into their amino acid components, peptide drugs are nearly always injected (a few exceptions, including the recently approved oral semaglutide, a GLP-1 medication, contain very high levels of the peptide and extra engineering because so much is lost to digestion).

Until recently, people in the pharmaceutical industry assumed that patients would not want to inject themselves regularly unless it was a dire situation such as uncontrolled diabetes or growth hormone deficiency, a childhood condition that leads to stunted growth if untreated, Long said.
“Injectables were thought to be for narrow patient populations. The industry thought that you couldn’t get millions of Americans to start injecting themselves,” he said. “The fact that GLP-1s have been so successful fundamentally upends that concept.”
Over the years, scientists have discovered many peptides that serve other purposes.
“The realization that people don’t mind injecting themselves opened up the space to 100 years of chemical and scientific history related to peptides,” Long said.