Retatrutide vs Mounjaro vs Wegovy: The Next Generation of Weight-Loss Medicine

You are weighing up three names: Wegovy, Mounjaro, and the newcomer everyone is talking about, retatrutide. You want to know which is best, and whether to start at all.

Here is the straight version. Two of the three are approved and can be prescribed to you right now, and we prescribe and monitor them. The third, retatrutide, has posted the strongest obesity-trial results reported so far, but it is still in trials and cannot be prescribed today.

They are not interchangeable. They work through different numbers of pathways, they shift different amounts of weight, and where you get them matters as much as which one you pick. Below is the honest comparison, so you can see where you fit.

How they actually differ

The simplest way to see it is one, two, three pathways:

• Wegovy (semaglutide) acts on a single hormone pathway, GLP-1. It was the first to bring dramatic medical weight loss to the mainstream.
• Mounjaro (tirzepatide) acts on two, GIP and GLP-1. Two levers, broadly, more effect.
• Retatrutide acts on three, GIP, GLP-1 and glucagon. It is a first-in-class triple agonist, and it is still investigational.

More pathways has meant more weight loss so far, but only two of these three are options you can start today.

Mounjaro vs semaglutide: what the real-world data show

Both work, but Mounjaro tends to deliver more. In a large real-world comparison of around 18,400 matched adults (JAMA Internal Medicine, 2024), people on tirzepatide were significantly more likely to reach meaningful weight loss than those on semaglutide: roughly 1.8 times as likely to lose 5% or more (a twentieth of body weight), 2.5 times for 10% or more (a tenth), and 3.2 times for 15% or more (about a seventh). At one year, the difference in weight change favored tirzepatide by about 7 percentage points.

We go into each of these medicines in more detail in Mounjaro & Wegovy: How Safe and How Effective Are They?, and cover how to protect muscle during treatment in GLP-1 Weight Loss and Muscle Loss.

Retatrutide: the new contender

The strongest results reported so far, but not yet something you can be prescribed. In topline Phase 3 results from the TRIUMPH-1 trial, announced by Eli Lilly in 2026 with the full peer-reviewed data still pending, adults with obesity on the highest dose lost on average about 28% of their body weight (more than a quarter of their starting weight), over 70 lbs, at 80 weeks, with many reaching reductions previously associated mainly with bariatric surgery (weight-loss surgery).

Read that with care: these numbers come from a topline company press release, not a full peer-reviewed publication, so treat them as promising rather than settled. Retatrutide is investigational and not yet approved. It is one to watch closely, not a treatment we or anyone else can prescribe today.

The part nobody advertises: the underground market

Buying these online is where the real danger is. Because demand outstrips supply, and because retatrutide is not yet approved, a gray market has grown around these compounds. They are sold as "research chemicals" and self-injected with no medical oversight. Unregulated product carries no guarantee of purity, dose accuracy or sterility. You do not truly know what is in the vial, how much, or whether it is contaminated.

Why prescribed, pharmacy-grade medicine is the safe route

For something you inject for months, a regulated medicine and a doctor watching over it are the whole point. Pharmacy-grade medicine is made to strict standards: verified purity, exact dosing, sterility and traceability. It is prescribed for your situation, dosed correctly, and monitored over time. An underground vial offers none of that.

How we approach it

We prescribe the approved options, monitor you properly, and adopt newer ones only when they are approved. At Longevity Marbella, medical weight loss uses regulated, approved medicines, prescribed and monitored by a doctor double board-certified in Internal Medicine and Endocrinology, and matched to you. As newer options such as retatrutide reach approval, we adopt them properly, never through the gray market.