Retatrutide vs Mounjaro: which works better for weight loss?

Mounjaro is the most potent weight loss injection on the market right now. But retatrutide, a new medicine that’s still being developed, might be even more effective.

So, which is better for weight loss? Read on to find out.

Key Takeaways

• In clinical research, retatrutide shows better results than Mounjaro
• But Mounjaro is the most potent weight loss medicine currently on the market
• Retatrutide is expected to become available in mid-late 2026

At a glance: retatrutide vs Mounjaro comparison

Let’s take a look at how these two medicines stack up.

Is Mounjaro the same as retatrutide?

Nope. Both medicines make you feel full, but they work in different ways.

Mounjaro weight loss injections mimic the behaviour of two hormones: GLP-1 and GIP. Whereas retatrutide works by bringing on the effects of three—GLP-1, GIP, and GCG. This triple action is what gives retatrutide a stronger effect.

In fact, retatrutide has driven better results in clinical trials than any other weight loss injection on the market.

Does retatrutide actually work?

From what we know so far: yes, retatrutide works very well.

Retatrutide is still being investigated in clinical trials, which means it isn’t approved yet. But the results we’ve seen are impressive.

Retatrutide vs Mounjaro for weight loss: results

Here's how the two medications compare at 68 weeks:

• Mounjaro: approximately 22% average weight loss
• Retatrutide: 28.7% average weight loss

Heads up: these are results from separate clinical trials so we can’t compare them head-to-head. But they can give us an idea of how well each medicine works.

Side effects and tolerability

Again, retatrutide isn’t approved yet, so there’s no official list of side effects. Though from what’s been reported in clinical research, retatrutide side effects are similar to Mounjaro’s:

• Nausea
• Diarrhoea
• Vomiting
• Constipation

This list isn’t exhaustive. Ask your provider if you’re worried about the side effects of weight loss medicine.

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."

Phoebe Fox - Weight Loss Specialist

Availability of Mounjaro vs retatrutide

You can get Mounjaro on the NHS (though you have to meet specific criteria and there may be waitlists) or via private prescription.

Retatrutide isn’t available on the NHS or anywhere else yet. Clinical trials are due to wrap up in May 2026, so we might see it on the market later that year.

If you want a closer look at how retatrutide compares with medicines that are already available or prescribed, you can read our guides on retatrutide vs Wegovy and retatrutide vs tirzepatide and semaglutide. And if you’re interested in how other emerging treatments compare, you can also see our guides on retatrutide vs mazdutide and mazdutide vs tirzepatide.

Which is better: retatrutide or tirzepatide?

This is a tough one, because there’s no “best’ weight loss medicine—there’s only what works for you personally. And remember, retatrutide isn’t available yet.

But there are really effective weight loss medicines that are already out there, such as Mounjaro and Wegovy, which you can get through Voy’s weight loss treatment. Your BMI is one of the key factors used to determine which option may be suitable for you, and you can use our BMI calculator to understand which treatments you may be eligible for.

Our team of clinicians will work with you to transform your lifestyle, so the weight stays off for good.

Take our quiz to see if you’re eligible.