Medications (in development)

For decades, effective medical treatments for obesity were limited. Lifestyle advice often focuses on willpower, overlooking the reality that weight is influenced by complex biology and genetics.¹ In recent years, weight loss injections such as Wegovy (semaglutide) and Mounjaro (tirzepatide) have changed the game, helping people lose between 15–20% of their body weight in clinical trials.²

A new name you might hear about is retatrutide, but it’s important to know this medication is still experimental. Early studies have shown some good results, with some participants losing nearly a quarter of their body weight in under a year.³ However, retatrutide is not approved, not available to the public, and not legal to obtain outside of clinical trials. So what exactly is it, how does it work, and why are researchers studying it so closely?

Can I get retatrutide yet?

The short answer: no.

While clinical trials for retatrutide are still ongoing, it’s important to be clear that this medicine is not available to the public anywhere in the world. If you hear of people getting hold of it, it’s almost certainly through black market channels. That comes with serious risks. Unlike licensed medicines, these products aren’t subject to strict testing or quality checks. They may be contaminated, made with unregulated ingredients, or dosed incorrectly, all of which could expose you to severe, and potentially life-threatening, side effects.

Retatrutide is still in the research phase. It’s currently being tested in large phase 3 clinical trials, expected to run throughout 2026, These studies are designed to confirm how well the drug works, how safe it is, and whether the promising results seen in smaller phase 2 trials can be replicated in larger groups.³ That means retatrutide isn’t licensed in the UK, EU, or US, and it isn’t available on the NHS or privately. If the upcoming trials continue to show positive results, it could be submitted for approval in the coming years.

What’s the theory behind retatrutide?

What makes retatrutide different from existing medicines is its “triple action”.

Current treatments like Wegovy and Mounjaro work by mimicking incretin hormones, natural chemicals released by the gut after eating that help regulate appetite and blood sugar. These hormones signal to the brain that you’re full, slow digestion, so food stays in the stomach longer, and help the pancreas release insulin when glucose levels rise.

• Wegovy (semaglutide) targets GLP-1 receptors only.

• Mounjaro (tirzepatide) targets GLP-1 and GIP receptors, giving it a “dual” effect.

Retatrutide activates three receptors at once:³

• GLP-1 receptors: reduce appetite, slow gastric emptying, and regulate blood sugar.GIP receptors: enhance insulin release and may improve fat metabolism.

• Glucagon receptors: increase energy use and fat burning, while also reducing appetite.

By targeting all three, retatrutide suppresses hunger and may also boost the body’s ability to burn stored fat. Researchers believe this combination explains why the results look so much more promising compared with earlier medications.³

How retatrutide is currently performing in studies

The most detailed results so far come from a phase 2 trial of 338 adults with obesity (BMI ≥30) or overweight with at least one weight-related condition (such as type 2 diabetes or high blood pressure). Participants received weekly injections of retatrutide or placebo for 48 weeks.³

Here’s what happened:³

• At 24 weeks, average weight loss was:

  • 7.2% with 1 mg

  • 12.9% with 4 mg

  • 17.3% with 8 mg

  • 17.5% with 12 mg

  • Compared to 1.6% with placebo.

• At 48 weeks:

  • 8.7% with 1 mg

  • 17.1% with 4 mg

  • 22.8% with 8 mg

  • 24.2% with 12 mg

  • Compared to just 2.1% with placebo.

To put that into perspective, the average weight loss with Wegovy (semaglutide 2.4 mg) is around 17.5% over 68 weeks, and with Mounjaro (tirzepatide 15 mg), around 20% over 72 weeks.^4,5

By the end of the study:³

• 100% of participants on the highest doses lost at least 5% of their body weight.

• Over 90% lost at least 10%.

• Up to 83% lost more than 15%.

These numbers raise the possibility that retatrutide could achieve weight loss comparable to bariatric surgery, but without the need for an operation. However, we must note that the patient cohort used in this study included both patients with and without diabetes, hence the results will not be applicable to everyone. 

Retatrutide side effects

As with all medicines, there are trade-offs. Retatrutide’s side effects look similar to those of other incretin-based treatments. The most common issues are gastrointestinal symptoms such as:³

• Nausea

• Diarrhoea

• Vomiting

• Constipation

• Abdominal discomfort

These side effects were dose-dependent; in other words, higher doses caused more problems. However, they were usually mild to moderate, and many improved over time. Starting with a lower dose and gradually increasing (a strategy already used with Wegovy and Mounjaro) helped reduce these effects.³

There was also an  increase in heart rate, which peaked at 24 weeks before declining. This will need to be studied further in larger trials to confirm whether it has any long-term significance.

A small number of participants had to stop treatment because of side effects.³

The safety of retatrutide

So far, retatrutide looks broadly safe, with side effects that mirror existing GLP-1 medications. 

But we should be cautious. The longest trial so far has only lasted 48 weeks. We don’t yet know what happens when people take retatrutide for two years or more, or how effective it is at maintaining weight loss in the long term.

Large-scale phase 3 trials will be essential to confirm both safety and effectiveness. No medicine is completely without risks, and how safe retatrutide is for you personally will depend on your health history, other conditions, and what medications you’re already taking.

When will retatrutide be available?

We predict that the earliest timeline is likely to be:

• 2025–2026: Completion of phase 3 trials.

• 2026–2027:  Possible FDA (US) approval.

• 2027 and beyond: UK approval by the MHRA and cost-effectiveness review by NICE.

So while retatrutide is generating excitement, it’s still several years away from being prescribed in the UK. Anyone taking retatrutide in the UK to date has not obtained their medication through prescription, and is most likely taking a compound version of the drug which may not be formulated properly, putting them at greater risk of dangerous side effects.

The numan take

Retatrutide is shaping up to be a promising obesity treatment. By targeting three hormones instead of one or two, it’s delivered great results in early trials. But it’s important to remember that this medicine isn’t available yet, and big questions remain about long-term safety and effectiveness. For now, treatments like Wegovy and Mounjaro remain the only options, alongside the building blocks of healthy eating, movement, and behavioural support.

1. ^{Adult overweight and obesity. NHS England Digital. https://digital.nhs.uk/data-and-information/publications/statistical/health-survey-for-england/2022-part-2/adult-overweight-and-obesity. Accessed August 27, 2025.}

2. ^{Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity. N Engl J Med. 2025;393(1):26-36.}

3. ^{Abdrabou Abouelmagd A, Abdelrehim AM, Bashir MN, et al. Efficacy and safety of retatrutide, a novel GLP-1, GIP, and glucagon receptor agonist for obesity treatment: a systematic review and meta-analysis of randomized controlled trials. Proc (Bayl Univ Med Cent). 2025;38(3):291-303.}

4. ^{Chao AM, Tronieri JS, Amaro A, Wadden TA. Semaglutide for the treatment of obesity. Trends Cardiovasc Med. 2023;33(3):159–66.}

5. ^{Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–16.}