Which weight loss injection is actually the best on the market right now?

The misconception worth clearing up first: there is no universally 'best' injection

The phrase 'best weight loss injection on the market' implies a single winner you can simply choose and order. That is not how prescription medicines work, and it is not how the evidence reads either. Both Mounjaro and Wegovy are licensed for weight management in UK adults with a BMI of 30 or above, or 27 or above alongside a weight-related condition such as high blood pressure, type 2 diabetes or obstructive sleep apnoea. Your medical history, any current medicines, how you respond to GI side effects and what previous treatments you have tried all influence which is appropriate. Our clinical team reviews every case individually, a named prescriber reads your consultation, not an automated system.

What the evidence does allow is an honest comparison of trial results. In SURMOUNT-1, tirzepatide at its 15mg dose produced an average body-weight reduction of around 20–21% over 72 weeks in adults with obesity. Semaglutide 2.4mg, in the STEP 1 trial published in the New England Journal of Medicine, produced around 15% average loss over 68 weeks. Neither figure is a guarantee for any individual. These are population averages from controlled trial conditions, real-world outcomes vary. You can read more about how the two injections sit against each other on our detailed comparison of the licensed weight loss injections.

Where tirzepatide's advantage over semaglutide actually comes from

Mounjaro (tirzepatide) is described as a dual agonist because it activates two receptors (GIP and GLP-1) rather than one. Both slow gastric emptying and reduce appetite, but the combined effect appears to produce stronger average weight loss. The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, put tirzepatide head-to-head against semaglutide 2.4mg in 751 adults with obesity over 72 weeks. Tirzepatide produced greater average weight reduction. That is the strongest direct evidence currently available. NICE's appraisal of tirzepatide (TA1026) also acknowledged that indirect comparisons favour tirzepatide over semaglutide at standard doses.

That said, semaglutide is not standing still. The MHRA approved a dedicated 7.2mg single-dose Wegovy pen in April 2026, a higher maintenance dose that trial data suggests produces around 20.7% average loss over 72 weeks, approaching tirzepatide 15mg results. So the gap is narrowing at the top of the dose range. Anyone asking what the best weight loss injection is today should account for this, the picture has shifted noticeably in just the last year. If you are trying to work out which weight loss injection is the right one for your situation, our guide walks through the key factors a prescriber will weigh up. Our guide to weight loss injections covers both medicines' dose schedules and how titration works in practice.

Eligibility, safety and what to expect alongside treatment

Both injections carry a Black Triangle (▼) designation from the MHRA, meaning they are under additional monitoring. The side-effect profile for both is predominantly gastrointestinal (nausea, loose stools, constipation, indigestion) most pronounced in the first few weeks or after a dose increase, and often settling with time. Serious but infrequent risks include acute pancreatitis; the MHRA highlighted this in a Drug Safety Update and advises seeking urgent help for severe stomach pain that reaches the back. Report any suspected side effects at the MHRA's Yellow Card scheme.

Neither medicine is licensed for use in pregnancy, while breastfeeding, or when trying to conceive. They are not licensed for under-18s. Women using oral contraceptives and starting tirzepatide specifically are advised to add a barrier method for the first four weeks of treatment and for four weeks after each dose increase, because the pill's absorption may be reduced, no equivalent advisory currently exists for semaglutide. These are details a prescriber goes through with you at the point of assessment, not things to navigate alone. If you want a sense of what a consultation covers, our frequently asked questions page is a good starting point.

Cost is often what shapes the question 'which is best' in practice. Private treatment for these medicines is priced per pen per month, and prices vary by dose and provider. For context on what the market actually looks like, our treatment pricing page sets out exactly what is included in a single transparent price (consultation, clinical review, delivery and aftercare) without a subscription. One thing worth knowing: if you are placing an order before 12pm on a weekday, dispatch can happen the same day, with DPD delivery the next working morning. That kind of speed matters to people, particularly those managing a busy schedule.

The question of which injection is 'best' is not one anyone can answer in a search result. It is answered in a clinical consultation. If you want to explore your options properly, some people find it helpful to read about the injections used in more significant weight loss cases alongside our page on understanding which injection works best for different people before speaking with a prescriber.