Weight Loss Injections in London: What the Clinical Evidence Actually Shows

What the large-scale trials measured, and why the numbers are real but not universal

The headline figures from the clinical trials are striking, and they come from properly controlled studies. In the SURMOUNT-1 trial, published in the New England Journal of Medicine, adults taking tirzepatide at the highest tolerated dose lost an average of around 20–21% of their body weight over 72 weeks alongside a reduced-calorie diet and increased activity. Semaglutide 2.4mg produced an average reduction of around 15% over 68 weeks in the STEP 1 trial, conducted under similar conditions.

A common misconception is that these figures represent the best-case patients, the highly motivated few. In fact the averages include the full trial populations, with all the usual variation in adherence and starting weight. Some people lost considerably more; some less. That spread is worth understanding before you start, because it shapes realistic expectations in a way that the headline number alone cannot.

In a more recent head-to-head comparison, the SURMOUNT-5 trial found tirzepatide produced greater average weight loss than semaglutide 2.4mg over 72 weeks in adults with obesity and no diabetes. NICE's appraisal of tirzepatide (TA1026) takes this evidence into account and recommends it for eligible adults within the NHS, though NHS access remains phased and criteria are strict.

The trials were not conducted in London specifically. Geography does not change how the medicine works. What does matter is individual health history, which is exactly what a prescriber weighs up.

Who is likely to be eligible, and how the BMI thresholds work in practice

For both medicines, the licensed eligibility follows the same basic shape: a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure, type 2 diabetes, high cholesterol, or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance, reflecting differences in how weight-related health risk presents. Our guide to weight loss injection eligibility sets out the full picture.

BMI alone does not determine whether treatment is appropriate. A prescriber also considers medical history, current medications, and whether there are any contraindications, including a personal or family history of certain thyroid conditions, pancreatitis, or other factors listed in the prescribing information. The assessment is not a formality; it is the point at which a clinician decides whether the medicine is genuinely right for you.

London residents accessing treatment privately do not need a referral. The process through a regulated online pharmacy involves a clinical consultation, identity and weight verification, and a prescription issued only if the prescriber is satisfied. You can read about how the clinical team at nume approaches that process, or review the credentials of our lead prescriber on the clinical team page.

NHS access versus private, what London patients are actually navigating

The NHS does prescribe both Mounjaro and Wegovy, but the practical picture for most Londoners is one of waiting. Wegovy is available through specialist weight management services under NICE guidance TA875, but those services carry significant waiting lists in most areas. Tirzepatide is being rolled out through GP practices under a phased commissioning plan, eligibility thresholds are high, and GP participation is optional, so availability varies considerably across London boroughs.

For people who do not meet the current NHS criteria, or who are not prepared to wait, private treatment through a GPhC-registered pharmacy is the legal alternative. It is worth understanding what that means in practice. You can verify any online pharmacy on the GPhC register before you hand over any personal information or payment. A legitimate pharmacy will always require a clinical consultation and a valid prescription before dispensing a prescription-only medicine. If a seller offers these medicines without that process, it is a serious warning sign.

Our guide to GP-prescribed weight loss injections explains the NHS route in more detail, including what to ask at your GP appointment. For a broader comparison of the available medicines, this overview of the three main weight loss injections covers how they differ in mechanism and evidence.

Cost context and what a realistic private treatment plan looks like

Private weight loss injection treatment is priced per pen, per month, and has shifted noticeably since Eli Lilly adjusted Mounjaro's UK list price in September 2025. Typical private prices since then range roughly £149–£375 per month depending on dose and provider, as widely reported. If you are weighing up your options, our guide to weight loss injections explains the medicines available and how each one works before you decide which route suits you. The dose you start on is the lowest available (2.5mg for tirzepatide) and the prescriber titrates upward on a schedule designed to let the body adjust before any increase. That process takes months, not weeks.

What those headline prices sometimes do not include is everything else: the consultation, the prescription fee, delivery, and ongoing clinical support. Our cost guide for weight loss injections breaks down what to look for when comparing services, and why those extras are not optional extras from a safety perspective. One transparent price that covers clinical review, dispensing and delivery is simpler (and safer) than a low headline figure with fees added at checkout.

If you would like to compare how London-accessible private services differ from what is available in other cities, there is a parallel guide covering weight loss injections in Leeds that covers similar ground. For answers to the questions our prescribers hear most often, the FAQs page is worth a look before your consultation.

If you are ready to find out whether treatment is suitable for you, the next step is a clinical consultation. There is no obligation, no referral needed, and no waiting list. Start your free consultation and a GPhC-registered prescriber will review your details the same day.