Retatrutide

Key points

• Retatrutide is a triple agonist: it activates the GIP, GLP-1 and glucagon receptors, where licensed drugs such as semaglutide act on one or two.
• In a phase 2 trial the highest dose gave an average weight loss of around 24 percent over roughly a year, though that is an early result from a single study.
• The phase 3 programme a licence would depend on is still underway, so it is not approved in the UK or anywhere else.
• In the UK it is available only to people taking part in a clinical trial.

Quick facts

What it is

Experimental triple hormone agonist (GIP, GLP-1, glucagon)

Studied for

Weight loss and obesity

Stage

Phase 3 trials underway; not licensed anywhere

UK status

Investigational; available only in clinical trials

In sport

On the WADA Prohibited List

How it works

Licensed weight loss medicines such as semaglutide and tirzepatide mimic gut hormones that curb appetite. Retatrutide adds a third target, the glucagon receptor, which is involved in how the body uses energy. The idea is that acting on all three at once could both lower appetite and raise energy use. How much each part contributes, and how it behaves over years rather than months, is still being worked out in trials.

What the evidence shows

The phase 2 results, published in a major medical journal, reported large average weight loss that rose with higher doses and had not clearly levelled off by the end of the study. That is a genuinely striking signal. What it does not yet show is how the drug performs in the larger, longer phase 3 trials regulators require, whether the weight stays off, or how it compares head to head with the medicines already licensed.

What it does not settle

• There are no completed phase 3 trials and no licence anywhere yet.
• Long term safety, and whether weight returns after stopping, are not yet known.
• Early weight loss is not the same as proven benefit for health outcomes such as heart disease.

Side effects

Common

• In trials the most common effects were stomach related, such as nausea, which is typical of medicines that act on gut hormones and tends to ease when the dose is raised slowly.

Less common but serious

• Because there is no licensed product, anyone using material bought online cannot know the dose, purity or contents. Counterfeit pens sold as retatrutide have been reported.

Report any suspected side effect through the MHRA Yellow Card scheme.

UK legal status and access

Retatrutide has no marketing authorisation, so it is not prescribed by registered clinics or pharmacies. In the UK the only route to it is a clinical trial. Products sold online are unlicensed and have not been through the checks that apply to a licensed medicine.

Common questions