How much weight should you be losing on Mounjaro — and what the evidence actually says

What SURMOUNT-1 actually found, and why the average isn't your target

The most cited figure from tirzepatide's phase 3 programme comes from SURMOUNT-1, published in the New England Journal of Medicine, which enrolled 2,539 adults with obesity but without type 2 diabetes. Over 72 weeks, participants at the 15mg dose lost an average of around 20–21% of their starting body weight. At 10mg the average was approximately 19%, and at 5mg around 15%. Those are the numbers people screenshot and share. What they rarely mention is the spread: some participants lost considerably more, others less, and in the first four to eight weeks, the change can feel imperceptibly slow.

The reason matters. Mounjaro starts at 2.5mg because the first pen is about tolerability, not transformation. Your system is adjusting to a medicine that slows gastric emptying and acts on two gut-hormone pathways involved in appetite and blood-sugar regulation. Meaningful weight loss tends to become more consistent as the dose increases and your body settles. If you're on 5mg and comparing your progress to someone else's plateau on 15mg, you're comparing different points on the same journey. Our clinical team's page on what weight loss looks like specifically at 5mg unpacks this dose in detail.

NICE's technology appraisal of tirzepatide, TA1026, uses these trial outcomes as part of its recommendation framework. If less than 5% weight loss is achieved after six months at the highest tolerated dose, continuing treatment is reviewed, which gives you a clinical benchmark, not a personal target set by a comparison website.

What UK private pricing for Mounjaro actually covers, and what it often doesn't

Private Mounjaro treatment in the UK is priced per pen, typically per four-week supply, and costs vary by dose and provider. Following Eli Lilly's list-price increase from 1 September 2025, private market prices reportedly range from roughly £149 at the starter dose to around £375 at the higher doses, though figures vary between providers. Those are the numbers you'll see quoted.

What they don't always tell you: some of those prices cover the pen alone. Consultation fees, prescription charges, dose-review support, aftercare and delivery can each be added separately. A headline monthly figure that looks competitive can become something quite different by the time all the components are included. Understanding how Mounjaro pricing works in the UK means looking at what a provider includes, not just the number at the top of the page.

At nume, we don't run the cheapest price in the market, that's a deliberate position. One transparent price covers your consultation, your prescription, your treatment, aftercare seven days a week and free next-working-day delivery. No subscription, no auto-renewal: every repeat order is reviewed by a prescriber before it goes out. When your pen arrives (tracked via DPD, in a plain box with nothing printed on the outside) the clinical review has already happened.

Why the cheapest listing is the wrong test for a prescription medicine

Mounjaro is a Prescription-Only Medicine. The only legal route to it in the UK is a prescription following a genuine clinical assessment. The MHRA has warned publicly about fake weight-loss pens sold online and via social media, counterfeit pens seized in UK enforcement operations have been found to contain insulin, creating a risk of serious harm. Large-scale seizures of illicit tirzepatide pens have occurred as recently as late 2025. A discount that bypasses proper prescribing isn't a saving.

The question to ask of any provider isn't whether they're cheaper; it's whether a GPhC-registered prescriber personally reviews each patient, whether the pharmacy is verifiable on the GPhC register, and whether the medicine comes through the licensed UK supply chain. Report any seller offering these medicines without a clinical assessment via the MHRA Yellow Card scheme. For guidance on how much tirzepatide to take and how dose decisions are made, that conversation belongs with a prescriber, our page on how prescribers approach Mounjaro dosing for weight loss explains the framework.

If you're weighing up Mounjaro against other medicines, the evidence page on expected weight loss with tirzepatide more broadly covers the comparative trial data, including the SURMOUNT-5 head-to-head results. And for the dietary side (because the medicine works best alongside real changes to what and how you eat) our guide to eating on Mounjaro is worth reading before your first pen arrives.

Starting a consultation with our prescribers

Mounjaro is licensed in the UK for 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 or type 2 diabetes. Lower thresholds apply for some ethnic backgrounds under UK guidance. BMI alone doesn't decide the outcome, a prescriber looks at your full picture, including any medicines you already take and any conditions that could affect suitability. Our clinical team includes GPhC-registered Independent Prescribers who personally review every consultation the same day it's submitted. There's no algorithm making that call.

You can explore the full range of weight-loss treatments available through nume on our weight-loss treatments overview, or go straight to the consultation. It's free, there's no obligation, and if treatment isn't right for you, we'll say so.