Mounjaro Vs Wegovy: Two Popular Weight Loss Treatments Compared

04 August, 2025  |  Jane Thomas - Marketing

There are some head-to-head rivalries that never seem to end. There's iOS vs Android. Coke vs Pepsi. PlayStation vs Xbox. And in the world of weight loss medication, there's the ongoing contest between Mounjaro and Wegovy, two of the industry's most popular weight loss injections. 

On the face of it, both of them work in similar ways; although they use different active ingredients, they both trigger the GLP-1 receptor in your brain, making you feel full and thereby suppressing your appetite. They're similarly priced, and they're available from the same pharmacists. So, how do you choose between them?

To help you make that choice, we've combed through the latest research and analysis to try and identify which of the two weight loss treatments is the most effective. Below, we'll not only cover the results of studies on the two drugs, but explain the differences between them and the ingredients they use, as well as the potential side effects they could cause.

Mounjaro vs Wegovy for weight loss: Which medication should I choose?

Before we dive into the specifics, let's briefly cover the differences between the way Mounjaro and Wegovy work. Although both injections act on the GLP-1 receptor we talked about earlier, making you feel more full, only Mounjaro acts on the GIP receptor.

The GIP (glucose-dependent insulinotropic polypeptide) receptor is responsible for supporting your body's fat metabolism and insulin sensitivity - and by inhibiting this hormone, Mounjaro is intended to limit your body's calorie intake as well as your appetite.

In theory, Mounjaro's dual-action approach should make it the more effective treatment. Instead of merely suppressing your appetite, it has the power to limit how many calories your body can absorb each time you eat a meal.

The difference between the two drugs is all down to the ingredients they use.

• Wegovy's main active ingredient is semaglutide…

• …while Mounjaro's key ingredient is tirzepatide. 

What studies tell us about the effectiveness of Mounjaro compared to Wegovy

In a recent study published in the New England Journal of Medicine, both semaglutide and tirzepatide were pitted against each other to assess their effectiveness.

A total of 751 people took part in the study, with an average weight of 113kg. None of them had type 2 diabetes, though some had conditions like high cholesterol or high blood pressure - both of which are commonly linked to obesity.

The study participants were placed on a high dose of either Mounjaro (tirzepatide) or Wegovy (semaglutide) for approximately 18 months, with injections taking place weekly as recommended. Here's what happened…

• Those who took semaglutide (Wegovy) lost 13.7% of their body weight on average across the duration of the study.

• But those on tirzepatide (Mounjaro) managed to shed 20.2% of their body weight on average - making it 6.5% more effective.

Body weight aside, those using tirzepatide (Mounjaro) slimmed down their waist size by more than 5cm in comparison to those using semaglutide. Plus, Mounjaro users on average had lower blood pressure, cholesterol and blood sugar levels when the study ended.

Although this study - published in May of 2025 - was the first time the two drugs had been directly compared against one another, previous independent studies have shown both Mounjaro and Wegovy to be effective treatments for weight loss.

However, the general trend seems to be that Mounjaro delivers more rapid weight loss than Wegovy. For instance, Mounjaro's clinical trial saw users lose an average of 15.7% of their body weight over an 18-month period, while those taking part in Wegovy's clinical trial lost 9.6% of their body weight.

It's important to note, however, that Wegovy's clinical trial was approximately two months shorter than Mounjaro's, which could have impacted the end result slightly.

Comparing Mounjaro and Wegovy side effects

Returning to the New England Journal of Medicine study, those using both Mounjaro and Wegovy experienced a similar amount of side effects. Between 77-79% of users in both groups experienced side effects of some kind, although only a handful had to stop using the injections as a result (6% for Mounjaro and 8% for Wegovy).

Again, more research is needed to get an accurate picture of the differences between the two treatments (this is the first time they were directly compared against each other, after all), but it appears that both Mounjaro and Wegovy have similar side effects - and that they occur at a similar frequency.

So, which weight loss treatment should I choose?

Before we jump to conclusions, it's important to point out that this study was created and sponsored by Eli Lilly, which is the company behind Mounjaro. Although it was peer-reviewed and published by a well-respected, independent medical journal, it can't be considered an independent study - and more research is still required to determine once and for all which weight loss treatment is the most effective.

At the end of the day, both Mounjaro and Wegovy (and rival drug Saxenda, for that matter) have all proved to be effective treatments. Our advice? Consult your pharmacist and ask their recommendation - different weight loss pens can be better suited to certain individuals than others.

If you're looking to get your weight loss journey off to the perfect start - and don't want to book a face-to-face appointment - explore our range of weight loss treatments and start your free online consultation with one of our pharmacists today.