There’s a new, hot weight loss injection making the rounds, and it’s become particularly popular among gym bros and other body-obsessives. What people are calling a “GLP-3,” retatrutide promises blockbuster weight loss results, helping people shed even more pounds than well-known GLP-1s like semaglutide (known as Ozempic and Wegovy) and tirzepatide (known as Mounjaro and Zepbound). And, word is that it doesn’t cause the same kind of muscle loss traditional GLP-1s are known for, explaining its boom among body builder types. Beyond weight loss alone, the drug seems like a promising solution to some chronic pain, appears to ease certain liver and kidney issues, and might mitigate certain heart health risk factors. 

All things considered, it seems like a miracle drug. So, what’s the downside? Well, it’s currently illegal. 

Retatrutide is still undergoing crucial safety trials by its manufacturer, Eli Lilly. While results so far have been promising, the drug is not currently FDA approved, and therefore may still carry unknown risks. Still, people are increasingly using black market retatrutide, ordering what they believe to be the drug from shady sources, which carries its own risk, separate from using a drug that hasn’t fully been safety tested. 

According to gym bro TikTok, many of retatrutide users are guys trying to get shredded, who say it’s a quick path to six-pack abs. There’s no real evidence quite yet that reta is any different than other GLP-1s when it comes to its impact on muscles, but we do know that it seems to be more powerful than other weight loss meds, which experts say could be dangerous for users who don’t have a significant amount of weight to lose—like gym bros.

So, why are already-lean guys taking a weight loss drug? Does it help you get abs? Is it safe even if it’s illegal? To get to the bottom of the current retatrutide boom, Playboy spoke to Dr. Spencer Nadolsky, a board-certified obesity medicine specialist, founder of Vineyard, a comprehensive weight management telehealth service, and a gym bro himself.

I’ve seen a few articles about the increasing use of retatrutide, an unapproved weight loss drug that people are accessing before it’s cleared for usage in the U.S. What is retatrutide?

Dr. Nadolsky: Semaglutide was one of the big groundbreaking [weight loss] medicines, which has been out as Ozempic [and now Wegovy] for quite a while, That is just a GLP-1 receptor agonist. GLP-1 receptor agonists have actually been out since 2005 with older versions of them that were shorter acting, and then they kept getting longer, more powerful.Then tirzepatide, or Mounjaro [and now Zepbound], came out. That one is a GLP-1 and GIP, glucose dependent insulinotropic polypeptide. Retatrutide adds on a third component: glucagon agonism. 

With semaglutide only, you see about 15 percent total body weight loss over a year or so. Tirzepatide is 20 or 21 percent total body weight loss. But with retatrutide, the thought is that it’s going to get close to— and we’re not sure exactly—but probably close to 30 percent over similar timeframes. So we’re talking bariatric surgery-like results. 

So it’s different from previous GLP-1s in that it’s more powerful?

Dr. Nadolsky:  It’s powerful. The GLP-1s and the GIPs are both powerful appetite suppressants. They work not only for reducing hunger, but also the thinking and wanting of food, which is why many people think it’s more powerful than the older obesity drugs that we had that worked for hunger. People think that these [drugs] are fat burners, but they aren’t. They basically help people eat fewer calories, for the weight loss effect anyway. They have other properties that help beyond weight loss and appetite, but for weight loss specifically, it’s just people eating fewer calories. 

[Retatrutide’s] glucagon component, though, seems to actually raise your metabolism and may help with specific fat oxidation in your liver.  I’ve had patients that have come from the clinical trials using it, then I have to put them on tirzepatide [once the trials are over] and they’re like, ‘oh man, this isn’t even anything close to as powerful as the retatrutide,’ which is actually insane because the tirzepatide is really powerful. 

Retatrutide is popular in the bodybuilding community, and for people who are concerned with body composition because reports are saying that it doesn’t seem to have the same muscle wasting effect that semaglutide and tirzepatide do. Is that true?

Dr. Nadolsky: It’s not known yet. This is why we have to wait for these phase three trials. And then to really know, you’d have to do a true head-to-head study. I don’t think it’s going to be muscle protective, but it’s probably going to be similar to tirzepatide. I would be worried about [retatrutide] specifically, though, just because of how powerful it is at making people lose weight quickly… just from the calorie deficit that it would create. 

You’ve had patients participate in clinical trials for retatrutide, but what are your thoughts on people accessing this medication through a sort of black market? Getting them before they are legal from potentially unknown sources?

Dr. Nadolsky: It’s potentially dangerous. There are reports of people getting pure retatrutide based on certain analyses, but you’re running the risk of unregulated companies with no FDA oversight. The other thing is, we still don’t have the full phase three results yet of the trials. We assume it’s going to be good and safe, but there could be some things that you might not know until these studies are out.

Let’s say [trials show] it is safe. [Ordering it from unapproved sources] you still run the risk of contamination and not knowing. You’d have to send off every batch to be analyzed every single time, and you’d have to get it from people that understand how to analyze these drugs to make sure there’s no precipitation of contaminants. Even if they try to make it right, you can precipitate certain things through the reactions of creating and manufacturing it, which can create basically things that are never intended to be in the product. So, I would never recommend it. I would never take it myself. I’ve never had a family member take it. But a lot of people are still taking it despite the potential risks. And I think that just goes to show how much people want to lose weight. They’ll take all sorts of risks just to lose weight.

A lot of people order compounded semaglutide and tirzepatide from telehealth companies, but that’s also not an FDA regulated product. I’ve heard similar caution from doctors around these medications, so it’s interesting that now we’re talking not just about unregulated versions of approved medications, but of something completely different.

Dr. Nadolsky: Yeah. And the thing is, they’re probably getting a lot of the real stuff in [the illicit retatrutide]. I just can’t say whether they’re getting other stuff in there. There could be contaminations. And again, you’d have to do batch analysis by people who really understand this stuff really well. And then on top of it, we just don’t know [about safety] yet. The phase three trials aren’t out. But it’s cheap. It’s really cheap. I understand why people do it. I just would never recommend it. 

Have you heard of any adverse events of people who are using the unapproved retatrutide? 

Dr. Nadolsky: Yes, but it’s really hard to know if those people would have gotten them with the FDA approved [medication], if it gets FDA approved. I’ve heard of people getting severe nausea, but we see those with the regular ones. We’ve seen hospitalizations, all sorts of different things like that. But, I haven’t heard of anybody getting a weird contaminant.

Any last words on retatrutide?

Dr. Nadolsky: We don’t have all the safety data from these drugs, like we do with the semaglutide and terzapatide. These drugs may be reserved for those who have much more weight to lose, so I would not be experimenting with the gray market versions, but I can’t stop you.