Are weight loss injections worth it for you?

What the evidence actually shows

The trial results for these medicines are genuinely significant. In the SURMOUNT-1 trial, adults taking tirzepatide at the highest dose lost an average of around 20–21% of body weight over 72 weeks, findings published in the New England Journal of Medicine. The STEP 1 trial showed around 15% average weight reduction for semaglutide 2.4mg over 68 weeks. Both are substantially larger effects than diet and exercise alone typically achieve in comparable timeframes.

Those figures come from tightly controlled studies with lifestyle support built in. Real-world results vary. Some people lose more, some less. A question our prescribers hear most weeks is whether the trials reflect what actually happens, and the honest answer is that consistent use alongside genuine lifestyle changes does produce meaningful results for most people, but the medicine is doing part of the work, not all of it.

The SURMOUNT-5 head-to-head trial (2025) found tirzepatide produced greater average weight loss than semaglutide 2.4mg directly compared. Both medicines are licensed for weight management in the UK; which one a prescriber recommends depends on your individual circumstances, not a league table. You can explore how these medicines compare in more detail on our page covering how well weight loss injections work.

Who these medicines are (and aren't) suited to

Eligibility under the licensed criteria covers adults with a BMI of 30 or above, or 27 and above with at least one weight-related condition such as high blood pressure, high cholesterol, prediabetes, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. Those figures are the starting point, not the whole picture; a prescriber looks at your full health history.

There are contraindications that rule these medicines out entirely. They are not recommended during pregnancy, breastfeeding or for anyone trying to conceive. They are not licensed for under-18s. A personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 requires a different conversation. Pancreatitis and certain gastrointestinal conditions also require careful prescriber assessment before starting. The safety profile of weight loss injections is well characterised, but it's one that a clinician needs to review against your circumstances.

NICE has appraised both medicines and set out the population most likely to benefit. Their guidance on tirzepatide (NICE TA1026) recommends it for adults with a BMI of 35 or above alongside at least one weight-related comorbidity. Private prescribing follows the licensed criteria, which are broader. If you want to understand the NHS eligibility picture, our overview of NICE guidance for weight loss injections covers the detail.

The cost and commitment question

Private weight loss injections are not cheap. Since Eli Lilly raised Mounjaro's UK list price in September 2025, typical private market prices run from roughly £149 to £375 per month depending on dose and provider. That cost recurs for as long as you're using the medicine, and for many people, that period runs to a year or more.

What you get for that spend varies considerably between providers. Some headline prices exclude the consultation, the prescription fee, delivery and any clinical support if something goes wrong. It is worth reading what is actually included before comparing numbers. You can find a breakdown of what drives pricing on our weight loss injection cost page.

The medicines also require genuine commitment to the process, and if you want a clear picture of how weight loss injections work in practice, including the injection routine, refrigerated storage and clinical check-ins involved, our dedicated page walks through each step. People who find it suits them tend to be those who treat the medicine as one part of a broader shift rather than a standalone fix. Worth being honest with yourself about that before you start.

Making the decision: what actually helps

The 'worth it' question comes down to three things: whether you meet the criteria, whether you understand what the medicine can and cannot do, and whether you have the right clinical support around you. A prescription-only medicine dispensed without a proper clinical assessment (sold online without a prescription from an unverified source) carries real risk. The MHRA has issued repeated warnings about counterfeit weight loss pens, some containing insulin rather than the stated ingredient. If you are still weighing up your options and want a straightforward explanation of what the weight loss injections are, including the difference between semaglutide and tirzepatide, our overview covers the essentials before you take things further. Buying through a pharmacy you can verify on the GPhC register is not optional; it's the baseline.

For people who do meet the criteria and use the medicine correctly, the evidence suggests weight loss injections can be a meaningful part of sustained weight management. For people who don't, the same evidence doesn't apply. That's exactly the kind of question a prescriber is there to work through with you.

If you'd like to explore whether treatment is suitable for your situation, speak to our prescribers, our free consultation is reviewed the same day by a GPhC-registered Independent Prescriber.