Looking to try weight loss medication? There are a few options out there. For example, the weekly injections Wegovy and Mounjaro, which are brand names for semaglutide and tirzepatide, respectively. And in the next year or so, a new medicine called retatrutide is set to be available as well.
All of these medicines make you feel full by acting like your body’s natural hormones. But they each do that in their own way.
If you’re exploring which weight loss medication might be best for you, it’s important to understand the differences between them. We’ve got you—here’s a head-to-head comparison of retatrutide vs tirzepatide vs semaglutide.
Key Takeaways
- Retatrutide targets three hormones (GLP-1, GIP, glucagon), tirzepatide targets two (GLP-1, GIP), and semaglutide targets one (GLP-1)
- At 68 weeks, retatrutide achieved 28.7% average weight loss, tirzepatide approximately 22%, and semaglutide around 17% on the highest doses
- Side effects are similar across all three medications, mainly digestive issues like nausea and diarrhoea
- Retatrutide is not yet approved and won't be available until mid-2026 at the earliest
- Tirzepatide (Mounjaro) and semaglutide (Wegovy) are both available now in the UK through NHS or private providers
What is retatrutide?
It’s a brand new weight loss medication that’s still being developed and is currently still in the clinical trial stage.
What sets retatrutide apart is that it mimics the behaviour of three hormones—GLP-1, GIP and GCG—rather than two (Mounjaro) or one (Wegovy). That’s why it’s sometimes given the nickname “triple G”. And this triple action suggests that it’s the most potent medicine of the lot.
Retatrutide is currently being investigated in clinical trials and isn’t due to be approved until at least mid-2026. But the results we have so far are impressive (more on that below!).
What is tirzepatide?
That would be the active ingredient in Mounjaro weight loss injections. It makes you feel full by bringing on the effects of the hunger hormones GLP-1 and GIP.
You might see Mounjaro being referred to as a GLP-1/GIP receptor agonist—which is just another way of describing how it works.
Mounjaro is approved in the UK as a treatment for weight loss and type 2 diabetes.
What is semaglutide?
And finally, we have semaglutide, the active ingredient in Wegovy and Ozempic.
These are two brand names for the same medicine. Semaglutide is called Ozempic when it’s used for type 2 diabetes (though Ozempic is sometimes prescribed off-label for weight management) and Wegovy when it’s used for weight loss.
Semaglutide acts like just one hormone, GLP-1. But it still works very well! If you take it for over a year alongside healthy lifestyle changes, you could lose around 17.5% of your starting weight. In a newer trial using a 7.2 mg dose, weight loss was up to 20.7% in people taking the higher dose for 72 weeks.
There’s also research into combining semaglutide with other hormones to boost weight loss further—such as CagriSema, which pairs semaglutide with cagrilintide for even more appetite control.
Key differences between retatrutide, tirzepatide and semaglutide
Okay, but how do these medicines compare? Let’s dive in.
How they work
Semaglutide, tirzepatide and retatrutide are all separate medicines that work in their own way. To give you a quick recap:
- Semaglutide acts like GLP-1
- Tirzepatide acts like GLP-1 and GIP
- Retatrutide acts like GLP-1, GIP and GCG
That means that they may all bring on different weight loss results (which is what the research shows).
Side effects
Because semaglutide and tirzepatide both act on the gut, they tend to bring on similar side effects. For both, the most common symptoms include nausea, constipation, vomiting, and diarrhoea.
How about tirzepatide and semaglutide vs retatrutide? There’s no official list of retatrutide side effects yet, because it isn’t approved. But it affects the gut, too. And in clinical research, the most commonly reported symptoms were the same as the above.
Side effects support at Voy
"If you're using Voy and you experience any side effects, rest assured that our expert clinicians are just a message or phone call away. They can adjust your dose, prescribe medication to ease your symptoms, or simply offer reassurance.
Everyone responds differently to weight loss treatment and we'll help you find what feels right for you."
Dosing
Though each of these medicines comes in different doses, they’re all weekly injections that are taken in a similar way.
For semaglutide and tirzepatide, you start on a low dose so that your body can adjust to the medicine, and then gradually move up to a higher strength every four weeks (provided that you aren’t getting any troublesome side effects).
It’s likely to be the same story for retatrutide, because that’s how it’s been taken in clinical trials.
Clinical data: semaglutide vs tirzepatide vs retatrutide
Now let’s take a look at weight loss results from clinical research.
Retatrutide
In the first phase 3 trial (TRIUMPH-4), participants lost an average of 28.7% of their body weight at 68 weeks on the highest dose (12mg), with the 9mg dose showing 26.4% weight loss. Earlier phase 2 trials showed 24.2% weight loss at 48 weeks, with 26% of participants losing at least 30% of their starting weight.
Tirzepatide (Mounjaro)
Based on results from a 72-week trial, estimated weight loss at 68 weeks is approximately 22% for the highest dose (15 mg).
Semaglutide (Wegovy)
At the current maximum approved dose of 2.4 mg, estimated 68-week weight loss is around 17.0%, based on data from the 72 week STEP-UP trial. However, using a 7.2 mg dose showed weight loss of up to 18% at week 48, suggesting that higher doses of semaglutide may help close the gap with other medications.
Curious how retatrutide compares with specific GLP-1s? Read our guides on Retatrutide vs Wegovy and Retatrutide vs Ozempic.
Which medicine is better for weight loss?
We’re asked this question a lot here at Voy. And it’s a tough one, because everyone can respond differently to medicines.
What’s most suitable for you depends on a bunch of factors, including your current health, medical history and your health goals. It also depends if you’ve tried weight loss medication before and whether you experienced side effects. Your provider will weigh all of that up when deciding which medicine to prescribe you.
This also feels like a good time to remind you that retatrutide isn’t approved yet, which means that a clinician can’t prescribe it to you. At the earliest, it might be available in mid-2026.
Ready to take the next step towards your health goals?
When combined with a healthy lifestyle, weight loss medication can be a gamechanger for some people. They can be a great option if you’ve tried to lose weight another way but didn’t see the results you hoped for.
You can get Mounjaro or Wegovy weight loss injections through our weight loss programme, plus dedicated support from our clinicians and coaches. We use a structured habit-change approach that’s backed by science and designed to transform your lifestyle.
Want to try it out? Take our short quiz to see if you’re eligible. Our clinicians will review and come back to you within minutes.
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