Prescribed weight loss injections: what the clinical evidence actually shows

What the landmark trials found, and what they mean for you

Prescribed weight loss injections earned their licences on the back of large, rigorous trials. In SURMOUNT-1, involving 2,539 adults with obesity and no type 2 diabetes, tirzepatide at its highest dose produced an average body-weight reduction of around 20–21% over 72 weeks. You can read the full paper via the NEJM SURMOUNT-1 publication. The STEP 1 trial for semaglutide 2.4mg reported an average reduction of roughly 15% over 68 weeks in a similar population.

These aren't small pilot studies. The SURMOUNT programme, combined with the SURPASS diabetes trials, involved well over 10,000 participants across the tirzepatide clinical programme. What the numbers consistently show is that, alongside a reduced-calorie diet and increased activity, these medicines produce weight loss that diet alone rarely achieves, and that the effect is meaningful enough to improve associated conditions like high blood pressure, elevated cholesterol and sleep apnoea.

One thing the trials also show clearly: results vary. The averages hide a wide range. Some participants lost substantially more; others less. A prescriber's job, in part, is to review whether you are in the group likely to benefit and to monitor whether benefit is occurring once treatment starts. If less than 5% weight loss is achieved after six months at the highest tolerated dose, NICE guidance suggests that continuing is reviewed. The medicine is a tool, not a guarantee.

Which prescribed weight loss injections are actually available in the UK?

Two medicines hold UK marketing authorisations for weight management in adults: Mounjaro (tirzepatide, by Eli Lilly) and Wegovy (semaglutide, by Novo Nordisk). Mounjaro is a dual GIP and GLP-1 receptor agonist, the only weight-loss medicine in the UK that activates both of these gut-hormone pathways. Wegovy works on the GLP-1 receptor alone. Both are given as once-weekly subcutaneous injections into the abdomen, thigh or upper arm, and both start at a lower dose to let your system settle before the prescriber increases it.

Ozempic is also semaglutide, but it is licensed for type 2 diabetes, not weight management. The NHS page on tirzepatide sets out a clear patient-level summary of how Mounjaro works, its common side effects and what to watch for. If you have seen Wegovy or Mounjaro discussed online and want to understand what is actually available and why, our overview of weight loss injections covers the landscape without the noise.

Saxenda (liraglutide) also holds a weight-management licence in the UK but is a daily injection and is not dispensed by nume. Our prescribers work with Mounjaro and Wegovy only, across their licensed dose ranges.

Who these medicines are (and are not) licensed for

The licence for both injections covers adults with a BMI of 30 or above, or a BMI of 27–29.9 alongside at least one weight-related condition such as type 2 diabetes, high blood pressure, raised cholesterol, obstructive sleep apnoea or cardiovascular disease. Lower BMI thresholds apply for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds under UK clinical guidance, because metabolic risk accumulates at lower BMI in these groups.

Neither medicine is licensed for under-18s. Pregnancy, breastfeeding and actively trying to conceive are all situations where these treatments are not recommended, your prescriber will ask about this directly. People with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 should not use these medicines; those with a history of pancreatitis require careful discussion.

BMI alone does not confirm suitability. That is why the clinical assessment exists. A prescriber looks at the whole picture: your current medications, your medical history, your goals. You can find a plain summary of eligibility routes (NHS and private) on our NHS weight loss injections page, or explore the private consultation route if you don't want to wait for an NHS referral.

NHS prescribed injections versus the private route, the honest picture

NHS-prescribed weight loss injections are available, but access is phased and criteria are strict. NICE recommends tirzepatide (TA1026) for adults with a BMI of 35 or above plus at least one weight-related comorbidity, delivered through a structured care pathway. The NHS England rollout is expanding in stages through 2025–2027, and from April 2026 some GP practices can prescribe under the new QOF contract, though participation varies by practice. For a full breakdown of what the phased rollout means in practice, the GP prescribing page explains who can prescribe and under what conditions.

For people who don't meet NHS thresholds, or who'd rather not join a waiting list, getting weight loss injections prescribed online through a legitimate private service is the legal alternative, provided a full clinical assessment is completed first. Every legitimate private route still requires a full clinical assessment, that is not optional, it is the law. At nume, a GPhC-registered Independent Prescriber reviews each consultation personally; a real clinician reads your answers, not software. Order before 12pm on a weekday and, once clinically approved, your treatment is dispatched the same day and delivered free the following working day via DPD. Details of what the consultation covers are on our treatment page.

If cost is part of your thinking, it is worth knowing what a legitimate private prescription actually includes, or should include. The weight loss overview covers the full picture, including what to look for and what to be cautious about when comparing providers. For the clinical side of who can issue these prescriptions, our page on this page on prescribers is the clearest starting point, and if you want to understand the full process from assessment to dispensing, our guide to doctor prescribed weight loss injections walks through each step in plain terms.