Results & Expectations

Retatrutide Results

Learn about Retatrutide results based on clinical trials, including expected weight loss, timelines, and how it compares to current treatments.

Whether you have seen retatrutide mentioned in news coverage and want to understand the published trial numbers, or are following its development from clinical trials towards possible approval, this guide explains what the early data show — and the important caveats around it. LetsLoseWeight is an independent comparison site; we do not prescribe medication.

Important: Retatrutide is an investigational medicine. As of this guide's last review, it is not licensed by the MHRA and is not available from regulated UK pharmacies. The numbers below come from the published phase 2 obesity trial. Phase 3 trials (the TRIUMPH programme) are ongoing and may produce different results. Anyone offering retatrutide for sale in the UK outside a registered clinical trial is doing so unlawfully. This guide is informational and does not promote use of retatrutide.

The headline number from the phase 2 trial

The retatrutide phase 2 obesity trial was published in the New England Journal of Medicine in 2023. Around 338 adults with obesity but without type 2 diabetes were randomised to placebo or one of several retatrutide doses for 48 weeks. All participants followed lifestyle interventions (Jastreboff et al., NEJM 2023).

Average weight loss at 48 weeks:

Dose Average weight loss Average weight loss in kg (≈)
Placebo 2.1% ~2 kg
Retatrutide 1mg 8.7% ~9 kg
Retatrutide 4mg 17.1% ~18 kg
Retatrutide 8mg 22.8% ~24 kg
Retatrutide 12mg 24.2% ~25 kg

The mean starting weight in the trial was around 108 kg.

How these numbers compare with currently licensed medicines

If you compare the headline averages at the highest doses across published trials:

  • Wegovy 2.4mg, 68 weeks (STEP 1): ~14.9% average weight loss
  • Mounjaro 15mg, 72 weeks (SURMOUNT-1): ~20.9% average weight loss
  • Retatrutide 12mg, 48 weeks (phase 2): ~24.2% average weight loss

Retatrutide produced larger average weight loss in less time than either Mounjaro or Wegovy in their respective pivotal trials. But these are comparisons across separate trials with different protocols, populations and durations — not within a single head-to-head study. They should be treated cautiously.

Why phase 2 data needs to be treated cautiously

Several caveats apply to any phase 2 trial result:

  • Trial size: Phase 2 trials enrol hundreds rather than thousands of participants. Rare events and outliers are harder to characterise.
  • Trial duration: The retatrutide phase 2 ran for 48 weeks. Weight loss in GLP-1-class medicines tends to slow noticeably between week 48 and week 72; the difference between retatrutide at 48 weeks and Mounjaro at 72 weeks is partly a duration effect.
  • Trial population: Phase 2 trial populations are often more homogeneous than phase 3 populations, which can flatter the result.
  • Phase 2 vs phase 3 results often differ: Larger, longer trials in more diverse populations sometimes show smaller average effects. Sometimes they confirm earlier findings; sometimes they don't.

The honest summary: retatrutide's phase 2 data is promising but provisional. Phase 3 data and post-marketing surveillance — neither of which currently exists — will give a more reliable picture.

What the spread looked like

The phase 2 trial averages compress a wide spread of outcomes. On the 12mg dose:

  • Around 83% of participants lost at least 15% of their starting weight
  • Around 63% lost at least 20%
  • Around 24% lost at least 30%

These proportions are higher than equivalent figures from Mounjaro or Wegovy trials, but again the cross-trial comparison should be treated cautiously.

What else changed in the trial

The retatrutide phase 2 trial reported on cardiometabolic markers alongside weight. By 48 weeks, the higher-dose retatrutide groups showed:

  • Reductions in waist circumference
  • Improvements in blood pressure
  • Improvements in lipid panel
  • Improvements in blood sugar markers in non-diabetic participants
  • Improvements in markers of liver health

Retatrutide is also being studied separately for type 2 diabetes and metabolic dysfunction-associated steatohepatitis (formerly NAFLD), reflecting the wider potential effects of triple GIP/GLP-1/glucagon agonism.

Side-effect signals from phase 2

Common side effects in the phase 2 trial were predominantly gastrointestinal — nausea, diarrhoea, vomiting, constipation — and broadly similar in pattern to Mounjaro and Wegovy. A small number of less common observations were flagged for further study in phase 3, including a signal around increased heart rate and arrhythmias at higher doses.

For more detail, see our retatrutide side effects guide.

What the phase 3 trials will tell us

The TRIUMPH programme is a series of phase 3 retatrutide trials for obesity, type 2 diabetes, sleep apnoea and metabolic dysfunction-associated steatohepatitis. Their results — when published — will:

  • Confirm or revise the average weight-loss numbers in larger, more diverse populations
  • Provide longer-duration data out to 72+ weeks
  • Better characterise rare side effects
  • Enable head-to-head comparison with Mounjaro in some settings

Until then, "retatrutide produces 24% average weight loss" is shorthand for "in a 48-week phase 2 trial with around 80 participants per dose group, the 12mg arm averaged 24%." That is real evidence, but it is not the same as the established, multi-thousand-patient datasets behind Mounjaro and Wegovy.

Why "buying retatrutide for the better numbers" is a bad idea

Some online sellers position retatrutide as a "next generation" alternative based on the phase 2 numbers above. From a results standpoint, this is misleading on multiple levels:

  • The product is not licensed anywhere in the world for weight management.
  • Unregulated supply has no quality assurance. The vials may not contain retatrutide, may be incorrectly dosed, or may be contaminated. The 24% average weight loss from the trial does not apply to whatever you've been sold from an unregulated source.
  • No clinical assessment is the standard before such purchases — meaning contraindications and other safety screens are bypassed.
  • No clinical safety net if something goes wrong.

The MHRA has warned consumers about buying weight-loss medicines without a prescription. The same warning applies — with extra force — to medicines that have not been approved at all.

When retatrutide might be available with confirmed results

If TRIUMPH phase 3 trials succeed, retatrutide will need to receive marketing authorisation from the MHRA, then go through NICE assessment for NHS use, then be supplied through licensed pharmacy channels. There is no published date. Anyone considering weight-loss treatment now should focus on the medicines actually available through regulated UK channels.

Frequently asked questions

Will retatrutide deliver 24% weight loss when it's licensed?
Quite possibly, but not certainly. Phase 3 trials in larger populations sometimes show smaller average effects than phase 2. The 24% figure is the phase 2 average at the highest dose; the licensed maintenance dose, the licensed schedule, and real-world results may all differ from that figure.

Should I wait for retatrutide rather than starting Mounjaro or Wegovy now?
Generally, no. There is no published date for retatrutide approval, the wait is likely to be measured in years, and the medicines that exist now are well-evidenced and effective. The decision is between a known treatment available today and an unknown treatment available at an uncertain future date.

Will retatrutide replace Mounjaro?
Unknown. If phase 3 data confirms greater weight loss with comparable side effects, retatrutide may become a preferred option for some patients. Mounjaro is also being further developed. Both are likely to remain available for the foreseeable future, with prescriber and patient choice between them.

Can I take part in a UK retatrutide trial?
Possibly. For UK trial sites, see the National Institute for Health and Care Research's Be Part of Research portal. Trial participation is the safest way to access an unlicensed medicine, with proper assessment, monitoring and follow-up.

Next steps

Sources

This guide is for general information only and is not a substitute for professional medical advice. Retatrutide is not currently approved or available in the UK outside clinical trials.

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Retatrutide Results: Phase 2 Trial Data Explained | LetsLoseWeight