Best Value Weight Loss Injections: What Clinical Evidence Tells Us

What the trials actually measured, and why it matters for value

The phrase "best value" tends to collapse into price comparison, but the clinical data suggest a different framing. The STEP 1 trial, published in the New England Journal of Medicine, followed 1,961 adults without diabetes over 68 weeks and found semaglutide 2.4 mg produced an average weight reduction of around 15%, compared with under 3% on placebo. SURMOUNT-1, the equivalent trial for tirzepatide, randomised 2,539 participants over 72 weeks and found average reductions of roughly 20–21% at the highest dose, and up to around 22.5% in some analyses. NICE's appraisal of tirzepatide (TA1026) noted that indirect comparisons favour tirzepatide, a finding since supported by the SURMOUNT-5 head-to-head trial, published in 2025, in which tirzepatide produced greater average loss than semaglutide 2.4 mg over 72 weeks.

What this means practically: if tirzepatide costs more per month but produces meaningfully greater loss, the cost per kilogram lost may actually be lower. That arithmetic is personal and depends on the dose you reach and how your body responds, but it is worth holding in mind when comparing prices. A medicine that costs 20% more and produces 30% more weight reduction is, by one reasonable measure, the better value option.

Worth checking: look at any quoted monthly price and ask whether it includes the clinical assessment, the prescription fee, delivery and ongoing prescriber review, or whether those are billed separately. A single transparent price is considerably easier to compare than a base rate with extras.

Which patients are eligible, and what shifts the calculation

Both medicines share broadly similar licensed eligibility criteria. Adults with a BMI of 30 or above qualify, as do adults with a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure, high cholesterol, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds can apply for certain ethnic backgrounds under UK guidance. The prescriber looks at the complete picture, not the number alone.

Eligibility shapes value because not everyone is suitable for both medicines. A history of specific conditions, current medications and individual tolerance all influence which option a prescriber considers appropriate. If one medicine is clinically preferable for you, the comparison between them becomes less relevant, the right choice is the one that is safe. Our guide to choosing the injection that fits your situation covers this in more depth.

NICE currently recommends tirzepatide for NHS use in adults with a BMI of 35 or above plus at least one weight-related condition, subject to a phased rollout. Those who do not meet NHS criteria, or who prefer not to wait, can access both medicines privately through a GPhC-registered pharmacy following a paid clinical consultation. Our overview of weight-loss injections explains the two routes side by side.

Where "cheap" becomes a warning sign

The MHRA has repeatedly warned that fake weight-loss pens are being sold online, sometimes through social media, without any clinical assessment. In October 2025, the first illicit UK manufacturing site producing counterfeit tirzepatide pens was raided. Separately, around 20 million doses of illegally traded weight-loss medicines, with an estimated street value of roughly £45 million, were seized across 2025. Some counterfeit pens have contained insulin, a risk that has led to hospitalisations. You can report suspected sellers through the MHRA's Yellow Card scheme.

Red flags for supply that is neither safe nor legal include offers to supply these medicines without a prescription, prices far below anything a licensed pharmacy could sustain, and discount codes from sellers you cannot verify. The GPhC publishes a public register of registered pharmacies, spending thirty seconds on the GPhC register before placing any order is a habit that costs nothing and could matter considerably.

For an overview of how providers compare on the evidence that actually counts, our guide to the best-rated weight-loss injections works through the clinical and practical differences in detail.

How to think about cost in the context of a prescription medicine

UK private pricing for weight loss injections, which are prescription-only medicines requiring clinical oversight, has shifted since Eli Lilly raised Mounjaro's list price from 1 September 2025. As widely reported, the highest-dose pen's list price rose from around £122 to around £330, and typical private prices since then range roughly £149–£375 per month depending on dose and provider. Those numbers are real, and they are not trivial.

The relevant question is what that price includes. A consultation fee paid separately, a prescription fee, delivery costs and the absence of aftercare support can add considerably to a base price. On a medicine that requires regular clinical review before each repeat, ongoing prescriber access is not an optional extra. If you are weighing up the options, our guide to finding the right weight loss injection for your circumstances sets out how to approach that comparison. For a fuller breakdown of what legitimate pricing covers, our treatment overview sets out what to look for.

At nume, the price for treatment covers the consultation, the prescription, delivery and seven-day-a-week aftercare with no separate charges and no subscription. We are not the cheapest option on the market, and that is deliberate. Our 2025 injection guide looks at what has changed in the market and what remains constant. If you would like a prescriber to assess whether treatment is appropriate for you, the starting point is a free consultation.

For anyone ready to take that step, check your eligibility and start your free consultation, a named GPhC-registered prescriber, not an algorithm, reads every submission the same day.