Which injection is considered the number one weight loss treatment right now?

The trial data that earned tirzepatide its top ranking

The SURMOUNT-1 trial, published in the New England Journal of Medicine, randomised 2,539 adults with obesity (but without type 2 diabetes) to either tirzepatide or placebo over 72 weeks. At the 15mg dose, average weight reduction reached around 20–21%. Those are figures the trial reported across thousands of participants, not outliers, not best-case scenarios. How weight-loss injections work in practice is worth reading alongside the headline numbers, because the mechanism helps explain why results vary between individuals.

Then came SURMOUNT-5, a head-to-head trial published in 2025 comparing tirzepatide directly with semaglutide 2.4mg over 72 weeks. Tirzepatide produced greater average weight loss, which is part of why it has earned recognition as the number one weight loss injection in current clinical evidence. NICE's appraisal committee noted this when updating TA1026 in September 2025, the formal recommendation that brought tirzepatide into NHS and private prescribing alike.

One misconception worth gently clearing up: these results are not produced by the injection alone. Every SURMOUNT participant followed a reduced-calorie diet and increased their activity alongside treatment. The medicine creates the conditions for change; it doesn't replace the lifestyle piece.

Where semaglutide (Wegovy) stands in the picture

Semaglutide is not a distant second. The STEP 1 trial (68 weeks, 2.4mg weekly) showed an average weight reduction of around 15%, which is substantially above what older medicines achieved. The NHS medicines page for semaglutide gives a clear patient-level overview of how it works and what to expect.

The 7.2mg dose, approved by the MHRA in April 2026 as a dedicated single-dose pen, narrows the gap with tirzepatide further still, trial data at that dose reported around 20.7% average weight loss over 72 weeks. For someone who has previously done well on semaglutide, or whose prescriber has clinical reasons to favour a GLP-1-only mechanism, Wegovy remains a clinically significant option, and our guide to weight loss injections starting with r explores some of the alternative options available in this category. Comparing the two in more depth is something our guide to choosing between weight loss injections covers directly.

Suitability is individual. A prescriber considers your medical history, existing conditions, any medicines you take and your weight-loss history before deciding which injection (if either) is appropriate for you.

What NICE eligibility criteria actually cover

Both medicines carry NICE recommendations, but the thresholds differ. Tirzepatide (TA1026) is recommended for adults with a BMI of 35 or above plus at least one weight-related comorbidity such as high blood pressure, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds apply for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds. The broader overview of weight loss injections on this site maps out the eligibility picture clearly.

For private prescribing (which is how nume operates) the licensed eligibility for both medicines is a BMI of 30 or above, or 27 or above with at least one relevant weight-related condition. A prescriber still reviews the full clinical picture; meeting the BMI threshold opens the door but doesn't guarantee the prescription.

If you're weighing up the cost side of things, our overview of what weight loss injection pricing actually includes explains what sits behind the headline figures, consultation, prescription, clinical review and aftercare all factor in. None of those should be optional for a prescription medicine.

How to approach choosing between them

The honest answer is that this is a conversation, not a ranking exercise. Evidence favours tirzepatide on average weight loss across populations. But averages are built from individuals, and your response depends on your physiology, your tolerance of side effects, your previous treatment history and what your prescriber finds when they review your case.

Side effects for both medicines are largely gastrointestinal, nausea, loose stools, reduced appetite, occasional reflux. These tend to be most noticeable early in treatment or after a dose increase, and settle for most people within a couple of weeks. The NHS tirzepatide page sets out the full side-effect profile in plain language.

Both are prescription-only medicines. The only legal route to either is a prescription following proper clinical assessment, our prescribers review consultations the same day. If you'd like to explore which option suits your circumstances, speaking to our prescribers is the natural next step.