Retatrutide Vs Mounjaro and Wegocy: Should you wait for the New Drug?
If you follow weight-loss injection news, you have likely seen information about retatrutide. Recent headlines include: “30% average weight loss” and “The most powerful obesity drug ever tested.” Many patients now ask whether they should wait for retatrutide or begin Mounjaro or Wegovy. A proper comparison between retatrutide vs Mounjaro is important, as the answer is often clearer than 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.
| Trial | Drug | Average Weight Loss |
|---|---|---|
| STEP 1 | Wegovy (semaglutide) | ~15% |
| SURMOUNT-1 | Mounjaro (tirzepatide) | ~22.5% |
| TRIUMPH-1 | Retatrutide | ~25% (up to 30.3% at highest dose) |
However, percentages alone can be difficult to interpret. Here is what these figures mean for someone weighing 120kg (18 stone 12 lbs).
| Medication | Weight Lost (kg) | Weight Lost (st / lbs) | % Body Weight Lost |
|---|---|---|---|
| Wegovy | ~18kg | ~2st 11lbs | ~15% |
| Mounjaro | ~27kg | ~4st 3lbs | ~22.5% |
| Retatrutide | ~30 to 36kg | ~4st 10lbs to 5st 9lbs | ~25 to 30% |
There is a measurable difference between Mounjaro and retatrutide. However, both medications are effective options. Mounjaro already achieves results that, five years ago, were only possible with bariatric surgery.
What Is Your Weight Loss Target?
This question is more important than which medication produces the highest trial results. Weight loss treatment is not focused on achieving a certain appearance or a “perfect” BMI. The goal is to reach your clinical target: the amount of weight loss that will significantly reduce your individual health risks.
This target may already be achievable with currently available medications. Here is what different levels of weight loss mean clinically.
| Amount of Weight Loss | Clinical Benefit |
|---|---|
| 3 to 5% | Meaningful reductions in blood glucose, triglycerides, and HbA1c |
| 5 to 10% | Improves blood pressure, lipid profiles, and sleep apnoea |
| 15kg or more | Can lead to full remission of type 2 diabetes, as shown in the DiRECT trial |
| 10 to 22% | What Mounjaro and Wegovy already deliver for most patients |
For most individuals, these targets can be reached with existing medications. Retatrutide offers additional benefit primarily for patients with a BMI above 50, severe complications, or resistance to current treatments. For others, the clinical target is already attainable.
We will discuss weight loss targets in detail in an upcoming post, including how targets are set during consultation, the Edmonton Obesity Staging System, and the best weight concept.
Are You Getting Everything Out of Your Current Medication?
Before considering retatrutide, it is important to address a key question. Most patients on Mounjaro have not reached the maximum licensed dose. Mounjaro is licensed up to 15mg weekly. Many patients plateau at 10mg without trying the highest dose.
Increasing to 15mg can result in an additional 3 to 5% weight loss for those who have stalled. Before considering a stronger medication, first determine whether your current treatment has been fully optimised.
Who Might Retatrutide Actually Be For?
Retatrutide will not be suitable for everyone, even after it becomes available. Current evidence suggests retatrutide will benefit patients with:
- Severe or treatment-resistant obesity, particularly a BMI above 50
- Metabolic liver disease (MASLD), where retatrutide has shown the largest liver fat reductions ever recorded for any drug
- Significant obesity-related complications such as severe sleep apnoea, osteoarthritis, or established cardiovascular disease
- Prior failure of multiple GLP-1 medications despite proper dose optimisation
For other patients, current licensed options remain highly effective and clinically appropriate.
The Cost Reality
This consideration is more significant than many patients realise. Mounjaro currently costs around £180 to £250 per month on private prescription in the UK. Early projections for retatrutide suggest a price of £800 to £1,500 per month.
This is 4 to 6 times more expensive for an additional 6 to 8% weight loss compared to a medication that is already highly effective. For most patients, this difference is unlikely to be clinically or financially justifiable.
Retatrutide Is Not Approved Anywhere Yet
This aspect is often overlooked in media coverage. As of 2026, retatrutide has not been approved by the FDA, the MHRA, or any regulatory body worldwide. It is still an investigational drug in Phase 3 trials. It cannot be legally prescribed in the UK outside a clinical trial.
Products sold online as retatrutide are unregulated, differ from the compound used in trials, and lack clinical safety oversight.
The realistic timeline for UK patients:
- Private prescribing: late 2027 to mid-2028 at the earliest
- NHS availability: 2029 at the earliest
For further information on retatrutide and current trial status, see our earlier post: Retatrutide: The New Weight Loss Drug Everyone Is Talking About.
The Key Points
- Retatrutide produces greater average weight loss than Mounjaro or Wegovy in trials. However, Mounjaro already delivers results close to bariatric surgery for many patients.
- The goal of treatment is to reach your clinical weight loss target, not the maximum possible reduction. For most patients, this target is already achievable with existing medications.
- Most patients on Mounjaro have not reached the maximum licensed dose of 15mg. Optimising current medication should be the first step.
- Retatrutide is most likely to benefit patients with severe or treatment-resistant obesity, metabolic liver disease, or significant obesity-related complications.
- Retatrutide is not approved anywhere in the world and is projected to cost £800 to £1,500 per month privately, making it unsuitable for most patients even when available.
What This Means For You
- If you are considering waiting for retatrutide, current evidence suggests a clear course of action. Begin treatment now with proven and available options.
- The difference between Mounjaro and retatrutide is real but modest. In contrast, delaying treatment by two years can have a significant impact.
- If you are already taking Mounjaro or Wegovy and your results have plateaued, a specialist review can determine whether your dose has been fully optimised before considering a change in medication.
- 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. Lilly’s triple agonist retatrutide delivered weight loss of up to an average of 71.2 lbs in first successful phase 3 trial. Press release. December 2025. https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-weight-loss-average
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
