Rachel Feltman: For Scientific American’s Science Quickly, I’m Rachel Feltman.

Today we’re doing a deep dive on an extremely hot topic: peptides. Hype around these basic chemical building blocks has infiltrated social media feeds and congressional hearings alike. To hear some folks tell it, various peptides can be used to solve just about any problem a human body could have. But the science on that is far from settled—and in the meantime the ready availability of gray-market peptides could put people in danger.

To help us understand why influencers seem so keen to inject themselves with dubious substances is Victoria Song, a senior reviewer at the Verge who writes the Optimizer newsletter.

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Thanks so much for coming on to chat today.

Victoria Song: Yeah, thanks for having me.

Feltman: So let’s start by talking about what peptides are and why it seems like they’ve been everywhere lately.

Song: Yeah, so a peptide is a building block of a building block: so proteins are made of amino acids, and peptides are just these short chains of amino acids. We’ve known about them for decades, but they are starting to gain a lot of traction in the biohacking community in Silicon Valley, and, you know, wellness influencers and fitness influencers have been kind of touting them as a new miracle cure-all for anything ranging from muscle aches to losing weight to skin care. So that’s a big reason why you see a lot of talk about peptides these days.

Feltman: Yeah, and GLP-1 is a peptide, right?

Song: Yes, so the P in GLP stands for “peptide.” The whole thing is glucagonlike peptide 1. [GLP-1] use has also made people a lot more comfortable with the concept of just injecting their own medications, which a lot of these peptides that people are buying online, they are in this powder form that they have to reconstitute with sterile water and then buy syringes off of Amazon and inject them into themselves.

Feltman: Yeah, and what you’re seeing people do online is different from, like, mainstream prescribed use of GLP-1s. But first, you went down a little bit of a rabbit hole with a peptide that a lot of people refer to as GLP-3. So could you tell us a little bit about that—how you got interested and what you found out?

Song: Yeah, so one of my editors messaged me, and he was like, “Oh, my God. The GLPs, they’re iterating like iPhones.”

Feltman: [Laughs.]

Song: “There’s a GLP-3.” And I was kind of like, “Uh, what do you mean, GLP-3?”

The official name for a GLP-3 is retatrutide. Retatrutide is currently under phase 3 FDA clinical trials by Eli Lilly. It is a triple agonist, which means it works on three different pathways.

And very, very early study results show that it’s even more effective than tirzepatide, which is the Zepbound and the Mounjaros. And so you have a lot of these fitness influencers procuring gray market—which means they’re not illegal sources; they’re in ...

Feltman: Mm-hmm.

Song: This gray area—of retatrutide. I was able to procure one off of a TikTok link ...

Feltman: Wow.

Song: From an influencer with an influencer code. It cost me about $130. And I got a little vial of something called retatrutide shipped to my house.

And it’s a little vial full of powder, and you mix it up with bacteriostatic or sterile water, and you can look up the dosage from other influencers online and peptide calculators online, and then boop, you inject it, no prescription necessary. And it was, like, a strange experience because this is not an approved weight-loss drug. This is something that is currently being studied for efficacy and safety. And while the results are promising, Eli Lilly’s not likely to be done with trials until sometime in late 2026.

Feltman: Mm-hmm.

Song: So I had procured this vial off the Internet in, like, late 2025. These kind of gray-market, dubiously sourced peptides, they are usually sold as, quote, unquote, “research only,” and it’s all across the sites, where it’s just like, “Wink, wink—don’t use this for human consumption. This is for research lab-grade materials only.” But it’s sort of like this legal gray area because the people who are selling these, they know that people are using them. And when you watch influencers talk about it, they’re not necessarily calling it retatrutide; they call it GLP-3 or reta or ratatouille to get around the social media kind of censors, where they get taken down for promoting an unapproved drug.

But it is something that is happening very widely in Silicon Valley. There are things called “peptide parties,” where you see a lot of, like, tech start-up founders who are just injecting a bunch of different gray-area peptides. And they’re just kind of biohacking and microdosing and coming up with their own mixes and matches from sometimes legitimate compound pharmacies, sometimes from very not legitimate compound pharmacies. And it’s taking an extreme treatment, which is, like, an injection, which is invasive, that has now become more normalized and treating it like a multivitamin. And we’re seeing a lot of that now.

Feltman: Yeah, you know, you mention compounding pharmacies. I would love it if you could just explain for our listeners how a standard compounding pharmacy is different from this sort of gray-market approach. Because like you said, the availability of GLP-1s through compounding pharmacies sort of normalized for people the idea that you might get sent something in the mail and, and inject it, but this is very different.

Song: Yeah, so generally, if you go to your regular pharmacy, you get the standard formulation of a drug or a pill. But there are people out there who may not be able to take those because they have an allergy to a preservative in the pill or there’s just something that they can’t, for whatever reason, use the standard formulation for. And so then their doctor will refer them to a compounding pharmacy that will mix it for them or make the drug for them custom. And these compounding pharmacies, they usually—they refer to something called a monograph, which is, like, a little recipe for these pharmacists to use the actual safe version of this drug to make for people.

And for a while there was a shortage of GLP-1 drugs, and so compounding pharmacies were then authorized by the FDA to make [GLP-1s], and that’s kind of where you saw all these telehealth services, like [Ro], Hims & Hers, jump on this bandwagon to get you these things. But when it comes to compounding pharmacies, some of them are registered with the state and licensed by the state and some do not.

So the quality you’re getting can vary widely. And it’s on the consumer to see which of these compounding pharmacies are at a very high standard and which are perhaps a little more dubious. But it can be very hard for the average person to really suss because some of these telehealth providers, they’re not actually pharmacies; they’re just distribution networks for compounding pharmacies.

Feltman: Right.

Song: So it can be very confusing. And then adding on top of that, the FDA said that these compounding pharmacies can’t do carbon copies of the [GLP-1] drugs anymore because there’s no longer a shortage. So some of them are now adding things that are, like, vitamin B12 to the formulation, and people don’t necessarily know how that’s gonna react in their bodies, and so they may be getting different effects than they’re expecting.

And separate from compounding pharmacies, there are what’s been referred to online as “Chinese peptides,” or peptides that are coming from suppliers in China that are, quote, unquote, “research only.” So there’s a lot of confusion as to, like, the sourcing of these more experimental peptides.

Feltman: Yeah, it’s funny—I was actually in a coffee shop a couple of weeks ago, and a couple of guys were working on a start-up pitch very aggressively out loud that seemed to boil down to them being like, “No one’s thought of this: We’re gonna make IV therapy bags full of peptides, and we’ll source them for people, and people will have a menu. We’ll take all the guesswork out. We’ll be able to tell them, ‘Oh, these are the effects you want. Here’s your IV bag.’” And they were, like, literally asking ChatGPT how compounding pharmacies work. So that was horrifying to me, and I think we’re gonna see a lot of scrappy businesses like that. But you’ve also reported on some big names who are kind of “peptide washing” and throwing around terms that they don’t understand. Is that right?

Song: Yeah, I recently wrote a story about I don’t know if Gwyneth Paltrow knows what a peptide truly is. Like, I know she’s heard of them. And I know she’s into injectables and IV therapies; like, she’s spoken about them widely. She’s talked about taking glutathione, which is a peptide. But just the way that she has talked about them, I’m just like, “Are you aware that peptides and injections are not necessarily the same thing?”

I can’t tell from some of the interviews she’s done. Like, she did one with Elle, and the way that that article was written, it defined NAD+ as a peptide. NAD+ is not a peptide. NAD is nicotinamide adenine dinucleotide. You’ll often see it marketed along with other peptides as NAD+, but it is not a peptide; it is a coenzyme, or a molecule that makes various enzymes more effective. It is associated with aging because it’s in every cell in your body, and your NAD levels, as you get older, naturally decline, and it’s associated with some aging-related conditions, like saggy skin, metabolic dysfunction. And on TikTok, for example, you’ll see a lot of people hawking NAD supplementation or NAD IV bags, NAD shots and pens.

And so she has this moisturizer through her Goop brand called—I believe it’s called Youth-Boost NAD+ Peptide Rich Cream. And I went through the ingredient list, and first of all, it doesn’t have NAD+; it has something called NMN, which is, like, [nicotinamide] mononucleotide, which is a precursor to NAD. And there’s only one single peptide listed in the entire ingredient list, and it’s at the very end of the ingredient list. And if you look at ingredient lists, generally, they’re listed by concentration, so that means it’s a trace amount, which does not feel like it’s a peptide-rich cream, in that respect. So it’s a standard moisturizer with a sprinkling of high-tech-sounding ingredients in there.

So, you know, I was basically writing about the “peptide washing” of that and how a lot of wellness products out here will sell you something, saying that it’s hopping on a very buzzworthy, trendy thing, so yeah.

Feltman: Well, there’s also, you know, like those guys I overheard in the coffee shop, this sense that if you can just cobble together the right peptides, it, it can do literally anything for you. And obviously, that’s almost certainly not true, but are there any potential risks in using any of these, beyond the risk of getting something that’s not a peptide at all from a dubious source?

Song: That’s something that’s being studied at the moment. You are seeing a lot of people online doing something called “stacking” these peptides. For example, one very popular one is called the “Wolverine” stack, and it’s a combination of a peptide called BPC-157 and TB-500. And all of these experimental peptides, they really sound like Star Wars droid names. And basically, what these peptides are purported to do is to help with tissue repair, wound healing, muscle recovery. So you see a lot of gym bros take it.

And then on top of the “Wolverine” stack, if you add GHK-Cu, which is a copper peptide, they call it the “glow” stack, and that’s supposed to do everything that the “Wolverine” stack does but also add skin care benefits, like improved collagen and elasticity and skin-firming qualities, if you add copper to it. But you maybe don’t want to DIY this. You can have copper toxicity from this. There is something called the “copper uglies,” where people don’t dose correctly, and it gives them the opposite effect on their skin, where it creates, like, adverse reactions in that sense.

But because so many of these peptides have not been rigorously studied for human use, we actually don’t know what some of the negative impacts could be. There are researchers who are really scared, or they’re concerned that it could actually cause cancer growth ...

Feltman: Sure, yeah.

Song: Or encourage cancer growth because some of these are growth-hormone analogues, and I believe one of them is, like, linked to pancreatic and other forms of cancer cell pathway growth.

And even with the [GLP-1] drugs, we’re still studying them right now. The vast majority of clinical research with these [GLP-1s] is for diabetics and obesity. There are a lot of studies going on right now about how they could impact things like polycystic ovary syndrome, fatty liver disease. There’s a lot of promise and hope, but the fact is that we don’t necessarily know how a lot of these drugs act in different conditions, which is why it can be hard to get them through traditional, safer routes.

And what you’re seeing with, “Well, I’m just gonna DIY it; I’m gonna get it myself,” is a real frustration with the health-care system because people are saying, “Oh, wow, look at how efficacious these things are. Look at how some people are saying it’s completely changed their lives. And I can’t get it. And the health-care system is not something that I’ve had a good experience with. I might as well just take a risk and go to these more dubious sources because I’ll do anything to have good health.” They are reacting to kind of the brokenness and the flaws in the U.S. health-care system and in terms of, like, access to affordable medication, or a lot of people go to doctors and they feel like they’re being churned through a factory.

So there is kind of a practical reason why this is happening. There is a lot of misinformation happening online as well. And a really huge narrative I see from influencers is, “These pharmaceutical companies don’t want you to have access to this because all they care about is their [patent] and their profit.” And there’s enough truth in that that they then use it to discredit medical institutions. And this is kind of how you get the wellness-to-MAHA pipeline happening.

Feltman: Yeah, well, and I’m glad you brought up MAHA. This is a great segue to [Robert F. Kennedy], Jr., who is very into peptides, I think because it lines up with all of the issues, tension around the current health-care paradigm that you outlined. So with this, you know, strong government support, what do you think that’s gonna mean for peptides?

Song: So in July the FDA is going to convene to discuss whether 14 peptides that were previously not approved for compounding use will get moved to a list that allows them to be compounded. But basically, RFK, Jr., has stated that he thinks it was illegal that the Biden administration took 19 of these peptides and said, “Hey, these are not safe for compounding use—we’re gonna move them to Category 2,” which is, like, you can’t use them in compounding unless the FDA gives express permission in a specific use case for the compounding. And moving them to Category 1 would mean that compounding pharmacies can go, like, “Hey, we’re gonna have a lot of access to these peptides then.”

He’s made the argument that by doing so, it’s a form of harm reduction. Because people are going to gray-market sources, because people are buying these peptides from China and perhaps are not doing a lot of research or third-party testing to check the purity of the things that they’re buying, if we bring it into a Category 1 bulk substance, then we can kind of make sure that reputable compounding pharmacies are selling these peptides. And if this ends up happening in July, I think the market will explode in a way that I don’t know that we’re necessarily prepared for.

There’s a high demand for peptides. There is distrust with the medical institutions. And some former FDA officials have said that RFK has mischaracterized their work. RFK has some very specific opinions about what the FDA should be doing. He has said something along the lines of it was illegal for the FDA to move those 19 peptides to the “You can’t use this for compounding” list because the FDA, in his words, is not meant to research efficacy; it’s only there for safety. And if it doesn’t kill you, you should be able to inject it if you want. So that’s kind of the logic he put out there, which is just fundamentally not what the FDA does. The FDA does study both efficacy and safety ...

Feltman: Right.

Song: And it advises based on those two factors. So there’s a lot of rhetoric happening, a lot of dismantling of trust in established institutions that is, like, very much wound up with this whole peptide craze.

I just wanna make it clear: Peptides are not inherently evil. Injections ...

Feltman: Right.

Song: Are not inherently evil. There is a time and a place for this. Insulin is the very first peptide that we synthetically found and is a lifesaving thing. [GLP-1s] have changed lives for many people. The way we are treating them in the mainstream biohacking culture needs more nuance. We’re seeing, like, a lot of these tendrils of peptide biohacking culture just seep into various areas of health and wellness, and it keeps me up at night.

Feltman: That’s all for today. We’ll be back on Monday with our weekly science news roundup.

Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Sushmita Pathak and Jeff DelViscio. This episode was edited by Alex Sugiura. Shayna Posses and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.

For Scientific American, this is Rachel Feltman. Have a great weekend!