Retatrutide is an experimental weight loss drug, but it’s not intended for “cutting” (which refers to a short-term phase of weight loss while maintaining as much muscle as possible).
Here’s what to know about retatrutide, fat loss, and preserving muscle.
Retatrutide fat loss: Does it actually burn fat?
First, a caveat: retatrutide is still being investigated in clinical trials and it isn’t yet available.
But from the data we have so far, retatrutide works very well at driving fat loss.
Most existing research on retatrutide focuses on total weight loss, not fat specifically. But in one phase 2 trial, people with type 2 diabetes taking 8mg retatrutide lost 26.1% of total body fat mass over a year.
Retatrutide works by mimicking the behaviour of three hormones. GLP-1 and GIP help reduce appetite and food intake, while GCG (glucagon) signalling may increase energy use and favour fat as a fuel source.
Is retatrutide suitable for a cutting phase?
No, retatrutide is not suited for cutting. In bodybuilding and fitness, a cut is a short, aggressive fat-loss phase after bulking.
Retatrutide is still in clinical trials and, if approved, would be licensed for chronic weight management in people who are overweight or living with obesity, rather than quick aesthetic changes in people without obesity.
This medication is designed for steady, long-term weight loss over many months, not rapid drops over weeks.
Does retatrutide cause muscle loss?
It’s normal to lose some muscle when you lose weight, even without medication. Diet and lifestyle changes alone can lead to a degree of muscle loss.
In the same phase 2 trial we just mentioned, people did lose some muscle on retatrutide. Though the proportion lost was similar to that on other weight loss treatments like tirzepatide and semaglutide.
Can you regain lost muscle mass?
The good news is that yes, you can regain lost muscle. Even better: you might see results in as soon as 6-8 weeks.
You’ll have to build muscle back up via regular strength training and eating a nutritionally balanced diet—including enough protein.
How to avoid muscle loss while promoting fat loss
You can (and should!) prevent muscle loss while losing weight. Here’s how:
- Do strength training. This can increase muscle strength and mass while improving your metabolism. Aim to do at least two sessions per week
- Get enough protein. It helps preserve lean body and muscle mass. Studies suggest eating 1.2–1.6 g/kg/day, distributed across 3–4 eating occasions.
Side effects during cutting: What to watch for
To be clear: don’t use retatrutide for cutting. But if you’re using it for weight loss, some possible side effects of retatrutide are:
- Nausea
- Diarrhoea
- Vomiting
- Constipation
These symptoms have been reported in clinical trials. Because research is ongoing, we’re still learning about retatrutide’s side effects. There’s no official retatrutide dosing schedule yet, either.
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."
Is retatrutide available in the UK?
Not yet. Retatrutide clinical trials are expected to finish in May 2026. So, we might see it on the market later that year.
But there are a bunch of other weight loss medications that are available right now. Through Voy’s weight loss programme, you can get orlistat weight loss capsules or injection pens (like Wegovy or Mounjaro weight loss injections) posted to you each month. You’ll also get lifestyle guidance from our team of clinicians.
We’re the UK’s leading medicated weight loss programme. Per our Voy weight loss results: our patients are twice as likely to meet their health goals.
Take our quiz to see if you’re eligible.
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