Retatrutide vs Mounjaro and Wegovy: Should You Wait for the New Drug?

• If you follow weight loss injection news, you have likely seen headlines about retatrutide.
• Recent headlines include “30% average weight loss” and “the most powerful obesity drug ever tested.”
• Many individuals now ask whether to wait for Retatrutide, or start Mounjaro or Wegovy now.
• A proper comparison between retatrutide and Mounjaro gives a clearer answer than the headlines suggest.

What the Numbers Actually Mean

• The trial results for retatrutide are genuinely impressive.
• Here is how the three drugs compare in headline trial results.

• There is a measurable difference between Mounjaro and retatrutide.
• Both medications are effective options in their own right.
• Mounjaro already achieves results that, five years ago, were only possible with bariatric surgery.

What Is Your Weight Loss Target?

• This question matters more than which medication produces the highest trial results.
• Weight loss treatment is not about achieving a certain appearance or a “perfect” BMI.
• The goal is your clinical target: the amount of weight loss that meaningfully reduces your individual health risks.
• This target may already be achievable with medication available today.

• For most individuals, these targets are reachable with medication already available.
• Retatrutide adds most benefit for individuals with a BMI above 50, severe complications, or resistance to current treatment.
• For everyone else, the clinical target is already within reach.
• We will cover weight loss targets in full in an upcoming post, including how targets are set in consultation and the Edmonton Obesity Staging System.

Are You Getting Everything Out of Your Current Medication?

• Before considering retatrutide, it is worth answering this question first.
• Most individuals on Mounjaro have not reached the maximum licensed dose of 15mg weekly.
• Many plateau at 10mg without ever trying the highest dose.
• Increasing to 15mg can add a further 3 to 5% weight loss for those who have stalled.
• Before considering a stronger medication, check whether your current treatment has been fully optimised.
• If your results have plateaued, this is worth discussing at a specialist review before assuming a switch is needed. Related reading: Why Does Weight Come Back After Stopping the Injections?

Who Might Retatrutide Actually Be For?

• Retatrutide will not be suitable for everyone, even once it becomes available.
• Current evidence suggests it is likely to benefit individuals with:

• Severe or treatment-resistant obesity, particularly a BMI above 50
• Metabolic liver disease (MASLD), where retatrutide has shown the largest liver fat reductions recorded for any drug to date
• Significant obesity related complications, such as severe sleep apnoea, osteoarthritis, or established cardiovascular disease
• Significant sleep apnoea specifically: a sub study within the TRIUMPH-1 trial reported a reduction of over 60% in breathing interruptions during sleep, from a severe baseline
• Prior failure of multiple GLP-1 medications, despite proper dose optimisation

• For everyone else, current licensed options remain highly effective and clinically appropriate.
• Not sure where you fall on this list? Am I Eligible for Weight Loss Injections in the UK? Covers eligibility for the medications available now.

What Are the Side Effects?

• The headline weight loss figures do not tell the whole story.
• Topline safety data from the TRIUMPH-1 trial gives a clearer picture of what to expect.

• Stopping treatment. Between 4 in 100 and 11 in 100 individuals stopped treatment because of side effects, depending on dose, compared with about 5 in 100 on placebo. 
• Dysesthesia. An altered or unusual skin sensation, affecting up to 12 in 100 individuals on the highest dose tested.
• Digestive side effects. Nausea, diarrhoea, constipation, and vomiting were reported, in a dose-related pattern similar to Mounjaro and Wegovy.
• Urinary tract infections. An increase in urinary tract infections was also observed and is being monitored in the ongoing trials.
• What this means. These are trial phase results, not a finalised safety label. If retatrutide is approved, the final product information may carry additional warnings once longer-term data is available.

The Cost Reality

• This is a bigger factor than many individuals realise.
• Mounjaro already represents a significant monthly cost on private prescription in the UK, and pricing has moved upward over the past year.
• Retatrutide is highly likely to launch at a considerably higher monthly cost again, in line with the premium pricing seen whenever a newer, more effective medication first reaches the market.
• For most individuals, this price gap is unlikely to be clinically or financially justifiable, particularly once existing medication has been properly optimised.

Retatrutide Is Not Approved Anywhere Yet

• This point is often lost in media coverage.
• As of 2026, retatrutide has not been approved by the FDA, the MHRA, or any regulatory body worldwide.
• It remains an investigational drug in Phase 3 trials and cannot be legally prescribed in the UK outside a clinical trial.
• Products sold online as retatrutide are unregulated, differ from the trial compound, and carry no clinical safety oversight.

• No application filed yet. As of July 2026, Eli Lilly has not submitted a New Drug Application to the FDA.
• Filing expected soon. Submission is expected in the final quarter of 2026 or the first quarter of 2027, once the remaining TRIUMPH trials report.
• Review takes time after that. A standard FDA review adds 6 to 10 months once an application is filed.
• Private prescribing: late 2027 to mid 2028 at the earliest.
• NHS availability: 2029 at the earliest.

For more on retatrutide and current trial status, see our earlier post: Retatrutide: The New Weight Loss Drug Everyone Is Talking About.

Common Questions

• Can I get retatrutide privately in the UK right now? No. It has no approval anywhere in the world and cannot be legally prescribed outside a clinical trial.
• Is it safe to buy retatrutide online? No. Products sold online are not the trial compound, are not regulated, and carry no safety oversight.
• What happens if I am already on Mounjaro when retatrutide launches? Nothing changes automatically. A specialist review at that point can compare your results so far against what retatrutide might realistically add.
• Will retatrutide replace Mounjaro and Wegovy? Unlikely for most individuals. It is expected to sit alongside existing options for a smaller group with more severe or treatment resistant obesity.

The Key Points

• Retatrutide produces greater average weight loss than Mounjaro or Wegovy in trials, though Mounjaro already delivers results close to bariatric surgery for many individuals.
• The goal of treatment is your clinical weight loss target, not the maximum possible reduction, and for most individuals that target is already achievable with existing medications.
• Most individuals on Mounjaro have not reached the maximum licensed dose of 15mg, so optimising current medication should be the first step.
• Trial safety data shows dose-related digestive side effects, dysesthesia, and a urinary tract infection signal, alongside the weight loss benefit.
• Retatrutide is most likely to benefit individuals with severe or treatment-resistant obesity, metabolic liver disease, or significant obesity related complications including sleep apnoea.
• Retatrutide is not approved anywhere in the world and is likely to cost significantly more than current options privately, making it unsuitable for most individuals even once available.

What This Means For You

• If you are considering waiting for retatrutide, current evidence points to a clear course of action: begin treatment now with proven and available options.
• The difference between Mounjaro and retatrutide is real but modest, while delaying treatment by two years can have a significant impact.
• If you are already on Mounjaro or Wegovy and your results have plateaued, a specialist review can check whether your dose has been fully optimised before considering a change.
• I assess your full clinical profile and work with you to find the right option for your weight, health history, and goals, with ongoing monitoring and support.

Author: Dr Imran Mughal, Private Specialist GP

Website: www.imclinic.co.uk

Book a consultation: https://notes.thanksdoc.co.uk/book/clinic/im-clinic

References

Jastreboff AM, Kaplan LM, Frías JP et al. Triple hormone receptor agonist retatrutide for obesity: a phase 2 trial. New England Journal of Medicine. 2023;389(6):514-526. https://www.nejm.org/doi/full/10.1056/NEJMoa2301972

Giblin K, Kaplan LM, Somers VK et al. Retatrutide for the treatment of obesity, obstructive sleep apnoea and knee osteoarthritis: rationale and design of the TRIUMPH registrational clinical trials. Diabetes, Obesity and Metabolism. 2026;28(1):83-93. https://dom-pubs.onlinelibrary.wiley.com/doi/full/10.1111/dom.70209

Bajaj HS, Welch M, Shah P et al. Efficacy and safety of retatrutide in people with type 2 diabetes (TRANSCEND-T2D-1). The Lancet. 2026;407:892-908. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(26)00967-0/abstract

Eli Lilly and Company. Lilly’s triple agonist retatrutide delivered powerful weight loss in pivotal phase 3 obesity trial. Press release. May 2026. https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-powerful-weight-loss

Eli Lilly and Company / American Diabetes Association 86th Scientific Sessions. Retatrutide TRIUMPH-1 topline phase 3 results and safety data. Presented June 2026.

Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). New England Journal of Medicine. 2022;387:205-216. https://www.nejm.org/doi/full/10.1056/NEJMoa2206038

Wilding JPH et al. Once weekly semaglutide in adults with overweight or obesity (STEP 1). New England Journal of Medicine. 2021;384:989-1002. https://www.nejm.org/doi/full/10.1056/NEJMoa2032183