Mounjaro is the UK brand name for tirzepatide, a prescription-only injectable medicine licensed for weight management and type 2 diabetes. In the largest weight-loss trial to date, SURMOUNT-1, adults without diabetes on the highest 15mg dose lost an average of around 22.5% of their body weight over 72 weeks alongside a reduced-calorie diet and more physical activity (New England Journal of Medicine, 2022). It is not a shortcut and it is not available to buy without a prescription. You can only obtain it in the UK after an online consultation and a clinical assessment by a prescriber.
This guide covers what Mounjaro actually is, how it works, who it is licensed for, the dosing schedule, the side effects worth knowing about, and how a regulated prescription works. Where we quote a number, we tie it to a named trial or regulator so you can check it yourself.
What is Mounjaro, and how is it different from Wegovy?
Mounjaro (tirzepatide) is what pharmacologists call a dual agonist. It mimics two of your body's own gut hormones at once: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). Wegovy (semaglutide) works on GLP-1 alone. That single difference is the reason the two medicines behave differently on the scales for many people.
The GLP-1 effect slows how quickly your stomach empties and dampens appetite, so meals keep you fuller for longer. It also quietens what many patients describe as "food noise" — the low, constant mental chatter about the next snack. The GIP effect adds a second layer that appears to improve how the body handles sugar and fat. Working together, the two signals reproduce a stronger version of the fullness cues your body already sends after eating.
Here is how the two headline medicines compare on the evidence, not on marketing:
| Mounjaro | Wegovy | |
|---|---|---|
| Molecule | Tirzepatide | Semaglutide |
| Hormone targets | GLP-1 and GIP | GLP-1 only |
| Key trial | SURMOUNT-1 | STEP-1 |
| Average weight loss in that trial | ~22.5% at 15mg over 72 weeks | ~14.9% at 2.4mg over 68 weeks |
| Form | Weekly injection | Weekly injection |
| Also a pill? | No | Not as the licensed Wegovy weight-loss product (oral semaglutide exists in other forms) |
The STEP-1 figure for Wegovy comes from a separate trial (New England Journal of Medicine, 2021). "Better" is not the right frame, though. These are averages from clinical trials, and your own response depends on your starting point, your health and how you live alongside the medicine. Some people tolerate semaglutide more comfortably; some do better on tirzepatide. A prescriber decides what fits you. If you want the direct head-to-head, we cover it in more depth in Mounjaro vs Wegovy.
One point of confusion worth clearing up: in the United States, Eli Lilly sells tirzepatide as Zepbound for weight loss and as Mounjaro for diabetes. In the UK there is no such split — Mounjaro is the single licensed brand for tirzepatide here. It is not worth chasing "Zepbound" from overseas sellers. Medicines bought outside the regulated UK supply chain carry a real risk of being counterfeit, wrongly stored or simply not what the label claims.
Who is Mounjaro licensed for in the UK?
Mounjaro was authorised for weight management in Great Britain by the Medicines and Healthcare products Regulatory Agency (MHRA), alongside its earlier diabetes licence. Its weight-management licence sets out who it is appropriate for.
For weight management, tirzepatide is licensed for adults with:
- a BMI of 30 or above (obesity); or
- a BMI of 27 or above where you also have at least one weight-related health problem — for example high blood pressure, type 2 diabetes, obstructive sleep apnoea, high cholesterol or non-alcoholic fatty liver disease.
Those thresholds are the licensed criteria. They are more generous than the tighter cohorts the NHS uses when deciding who it will fund, which is a separate question about public spending rather than about whether the medicine is right for a private patient. Lower thresholds may also apply for some ethnic backgrounds — including people of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean family origin — because cardiometabolic risk can appear at a lower body weight. A prescriber will factor this into your assessment.
There are also situations where Mounjaro is not suitable. It should not be used in pregnancy or while breastfeeding, and it is not licensed for under-18s for weight loss. A personal or family history of medullary thyroid cancer or the syndrome MEN 2, or a history of pancreatitis, are flags a prescriber needs to know about. This is exactly why an honest medical history matters more than a fast approval — full detail on who qualifies is in Am I eligible for Mounjaro?.
The Mounjaro dosing schedule: 2.5mg to 15mg
Mounjaro is a once-weekly injection you give yourself, usually with a pre-filled pen. You do not start at a high dose and you cannot safely jump to one. The medicine follows a titration schedule — a gradual step-up that lets your body adjust and keeps side effects manageable.
The standard pattern is:
| Phase | Dose | Typical duration |
|---|---|---|
| Starting (induction) | 2.5mg once weekly | At least 4 weeks |
| Step up | 5mg once weekly | At least 4 weeks |
| Continue stepping (as needed) | +2.5mg increments (7.5mg, 10mg, 12.5mg) | At least 4 weeks each |
| Maximum | 15mg once weekly | Maintenance |
The rules behind the table matter. The 2.5mg starting dose is an induction dose: its job is to introduce tirzepatide to your system gently, not to drive dramatic weight loss. If the scales barely move in month one, that is expected. Increases happen in 2.5mg steps and no sooner than every four weeks, up to a maximum of 15mg. Rushing the steps is the quickest route to feeling genuinely unwell.
Not everyone needs to reach 15mg. Plenty of people find a comfortable, effective "maintenance" level at 5mg, 7.5mg or 10mg — steady progress with tolerable side effects is the goal, not the highest number on the pen. If you miss a dose, take it within four days of your usual day; if more than four days have passed, skip it and resume on your normal day, and never double up. We go through the full step-by-step schedule, missed doses and plateaus in the Mounjaro dosage guide.
Side effects: what's common, and what's serious
Every effective medicine has trade-offs, and Mounjaro is no exception. Most side effects are gastrointestinal and tend to be mild, appearing in the first days after an injection or after a dose increase, then easing as your body adapts.
The common effects include:
- nausea
- diarrhoea or constipation
- indigestion and reflux
- reduced appetite
- tiredness
These are usually manageable. Eating smaller portions, chewing slowly, keeping meals lower in fat and staying hydrated between meals all help; we cover the practical detail in foods to avoid on Mounjaro and unpack the full list in the Mounjaro side effects guide.
Some effects are serious but rare, and they are the reason clinical oversight is not optional:
- Pancreatitis (inflammation of the pancreas). Severe, persistent abdominal pain — often spreading to the back — needs urgent medical attention.
- Gallbladder problems, including gallstones, which can occur with rapid weight loss.
- Low blood sugar (hypoglycaemia), more likely if you also take insulin or a sulfonylurea for diabetes.
- Dehydration from prolonged vomiting or diarrhoea.
One practical point that surprises people: because Mounjaro slows stomach emptying, it can reduce the absorption of oral contraceptive pills, particularly when you start or step up your dose. If you rely on the pill, a barrier method such as condoms for four weeks after starting and after each increase is a sensible precaution.
If you experience a side effect, report it. The UK's Yellow Card scheme (yellowcard.mhra.gov.uk) lets patients and clinicians flag suspected reactions directly to the MHRA, which is part of how the safety of any medicine is monitored after licensing. And always speak to your prescriber before you start, stop or change treatment.
How it works at The Weight Clinic
The Weight Clinic is a GPhC-registered UK online pharmacy, not a subscription app. Care is overseen by our Superintendent Pharmacist, Andrew Lane, with prescribing by registered independent prescribers, and every request is reviewed by a real clinician rather than an automated approval.
The route is straightforward but properly clinical. You complete a secure online consultation covering your height, weight, medical history and current medicines. A prescriber reviews it against the licensed criteria and either issues a private prescription or, where the medicine isn't appropriate, explains why. If approved, Mounjaro is dispensed from a regulated UK pharmacy and sent in cold-chain packaging — tirzepatide is a peptide that must be kept refrigerated between 2°C and 8°C to stay effective, so it travels with insulation and cool packs, and the detail on keeping it stable is in how to store Mounjaro.
On pricing, we keep it plain: Mounjaro from £125 a month, with a free eligibility check and no subscription lock-in — you reorder when you need to. Wegovy is also available, with a first month from £80 (standard £115, with £35 off your first order using code NEWME).
If you would like to know whether Mounjaro is a fit for you, the honest first step is a clinical assessment.
Check your eligibility for Mounjaro →
You can also read more on the Mounjaro treatment page, compare the full range on weight-loss injections, or browse all treatments. For a fuller walkthrough of the process from questionnaire to delivery, see how to get Mounjaro in the UK.
A realistic view of results
The SURMOUNT-1 figure — around 22.5% average weight loss at 15mg over 72 weeks — is genuinely striking, but three caveats keep it honest. First, it is an average: some people lost considerably more and some less, and results vary from person to person. Second, it was achieved alongside diet and activity changes, not instead of them; the medicine reduces appetite, but what you eat still counts. Third, obesity is a long-term condition, and appetite and "food noise" often return if treatment stops — which is why maintenance and lifestyle strategy, not a quick course, are the real objective.
Used well, within a regulated service and with realistic expectations, Mounjaro is one of the most effective weight-management tools currently available in the UK. Used carelessly — rushed titration, unregulated pens, no clinical review — it becomes a risk rather than a benefit. The difference is oversight.
Ready to see where you stand? Check your eligibility with a UK-registered pharmacy.
Frequently asked questions
How much weight can you lose on Mounjaro?
In the SURMOUNT-1 trial, adults without diabetes on the highest 15mg dose lost an average of around 22.5% of their body weight over 72 weeks, alongside a reduced-calorie diet and more physical activity. That is a trial average — results vary from person to person, and the figure was achieved with lifestyle changes, not instead of them.
Can I buy Mounjaro without a prescription in the UK?
No. Mounjaro (tirzepatide) is a prescription-only medicine. In the UK it can only be supplied after an online consultation and a clinical assessment by a prescriber, who checks it against the licensed criteria. Buying from sellers who skip that step means the product may be counterfeit, wrongly stored or not what the label claims.
Who is Mounjaro licensed for in the UK?
The MHRA licence for weight management covers adults with a BMI of 30 or above, or a BMI of 27 or above if they also have a weight-related health problem such as high blood pressure, type 2 diabetes, obstructive sleep apnoea, high cholesterol or non-alcoholic fatty liver disease. These are more generous than the tighter cohorts the NHS uses for funding decisions. A prescriber makes the final call.
What is the Mounjaro dosing schedule?
Mounjaro is a once-weekly injection that follows a titration schedule. You start at 2.5mg for at least four weeks, then step up in 2.5mg increments no sooner than every four weeks, up to a maximum of 15mg. Not everyone needs the highest dose — many people settle at an effective maintenance level of 5mg, 7.5mg or 10mg.
What are the side effects of Mounjaro?
The most common effects are gastrointestinal — nausea, diarrhoea or constipation, indigestion, reduced appetite and tiredness — and usually ease as your body adapts. Rarer but serious effects include pancreatitis, gallbladder problems, low blood sugar and dehydration. Report any suspected reaction through the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk, and speak to your prescriber before starting, stopping or changing treatment.
How much does Mounjaro cost at The Weight Clinic?
Mounjaro starts from £125 a month, with a free eligibility check and no subscription lock-in — you reorder when you need to. Wegovy is also available, with a first month from £80 (standard £115, with £35 off your first order using code NEWME).
