Everyone's talking about peptides. So what are they, ...

Peptides are seemingly everywhere right now. From influencers touting their ability to help you recover from workouts faster, build muscle and get smoother skin to celebrities spilling their secret "stacks" of injectables — peptides are the latest wellness craze. But, in the words of Substacker Juliana Ramirez, who writes a newsletter about search terms: "Wtf is a peptide."

Naturally, that raises some follow-up questions: Are they safe? Do they even work? The answers are a bit complicated, so I spoke to experts to help make sense of it all. 

What are peptides? 

All peptides are short chains of amino acids — tiny molecules that are the "building blocks of life." But that's about all they have in common with one another. Your body naturally makes thousands of peptides, and each one does something different. Some keep blood pressure steady. Others tell the immune system when to ramp up to fight infection and when to back down. And still others regulate stress. 

Right now, the big hype is around injectable peptide medications, which are made in labs to mimic naturally occurring ones, often tweaked to last longer or have stronger effects. 

Some peptides you've likely heard of, from injectable insulin to GLP-1 medications like Zepbound (tirzepatide) and Ozempic (semaglutide), which help with diabetes and weight loss; these drugs are approved by the U.S. Food and Drug Administration (FDA) and are backed by years, if not decades, of research showing that they're safe and effective.

Other peptides — like compounded semaglutide and compounded tirzepatide — exist in a kind of gray area because they're essentially copies of the approved medications, but are less regulated.

There are also injectable peptides that are unregulated, largely untested in humans and basically experimental — these are the ones garnering a lot of attention right now. They include the "Wolverine stack" (a combination of BPC-157 and TB-500) that promises faster healing; CJC-1295 and Ipamorelin, which claim to promote muscle growth, fat loss and better sleep; Melanotan II for sun-free tanning; and copper peptides (GHK-Cu) that claim to reduce wrinkles and stimulate hair growth. 

What the heck is a peptide stack?

As peptides — especially less regulated ones — become more popular, some people are taking several at once. A "stack" is a term from the biohacking and bodybuilding worlds, which refers to taking a combination of different treatments.

The idea is that the compounds work together for better results, but scientists haven't studied whether this is true. And, Patel says, it adds another layer of risk. "If you're stacking multiple peptides, you have no idea which peptide is doing what for you and there's no way to know if you're really safe," he explains. Yet, even some of Patel's friends, who are "regular dads like I am" are now stacking, he says.  

Do they work? 

That really depends on which peptide we're talking about. 

Ozempic, Zepbound and other GLP-1 medications are highly effective because they regulate blood sugar, appetite and digestion. Those functions are important for maintaining a healthy weight, which, in turn, affects the risk of health conditions such as diabetes, heart disease, kidney and liver problems and arthritis. The GLP-1 hormone also acts on the brain's reward centers, helping to curb appetite and possibly addictive behaviors too.

But not all peptides are as potent or well-studied. "Just because this one peptide has earned its reputation as this sophisticated mind-body drug doesn't mean that all peptides are the same," Dr. Lucy McBride, a primary care physician and author of the forthcoming book Beyond the Prescription, tells Yahoo. "But the other peptides got a big image boost [from the success of GLP-1s] when, in fact, they're not all created equally."

OK, so why are people taking them? 

Everyone from Joe Rogan to Jennifer Aniston has said they're using injectable peptides for antiaging and anti-inflammatory benefits, for better workout and injury recovery, for improved metabolism, or just to feel better. 

McBride sums it up: "The word 'peptide' has become synonymous with being inevitably good for you, which is just not true." 

That said, she acknowledges that there are many unknowns, and the currently unregulated peptides might work. "Science is an iterative process" — meaning it's always testing and refining — "and maybe someday we'll be recommending the Wolverine stack," she says. But, to her mind, we don't know enough yet.

What are the risks of unregulated peptides? 

Because each peptide does something different, they each carry their own unique risks. But again, experts don't know for sure because these unregulated peptides haven't been studied in humans.

For example, scientists fear that Melanotan II and BPC-157 could fuel the growth of certain kinds of cancers, experts tell Yahoo. Too much growth hormone can also put a dangerous strain on the heart.

There's also the risk of taking an unknown dose of an unregulated substance — or a combination of them. Without testing, there's no guarantee that you're getting the peptide you ordered, that it isn't contaminated or that it's the right dose. One study found high rates of contamination and incorrect dosing among GLP-1s ordered from online pharmacies. And those risks go up when people start stacking multiple peptides. 

How are people getting these peptides if they're not FDA-approved? 

Wellness clinics are selling unapproved peptides labeled "R&D only" to indicate they're intended solely for research. That frees them from liability, even if people are clearly buying peptides to use on themselves.

The FDA tightly regulates drugs, but the research chemicals used to make them exist in a legal gray area. They carry labels like "not for human consumption." There technically aren't laws preventing people or companies from buying them and turning them into injectables — though that hasn't stopped the FDA from issuing warnings about these drugs. Once a peptide vial is in a consumer's hands, it's their choice what to do with it. "You are truly experimenting on yourself when you take these things," Dr. Vikas Patel, founder of MD Longevity Lab, tells Yahoo — and there's no law against that.

And it may soon become even easier to get these peptides. Health Secretary Robert F. Kennedy Jr. has called on the FDA to loosen restrictions on the injections. Starting in July, regulators will meet to evaluate 12 peptides and decide whether compounding pharmacies should be cleared to manufacture and sell them.

"I hope that it will create more opportunity for FDA regulation and rigor because I think this is the problem with a lot of this peptide junk out there: It's unregulated, and it's under-tested," Dr. Cate Varney, an obesity medicine specialist with the University of Virginia, tells Yahoo.