Mounjaro (tirzepatide) and Ozempic (semaglutide) are both weekly injections, but they are not the same medicine. Mounjaro activates two gut-hormone receptors (GLP-1 and GIP), while Ozempic activates one (GLP-1). Importantly, Ozempic is licensed in the UK for type 2 diabetes — not for weight management — so this comparison is really about understanding the active ingredients and the products actually licensed for weight loss.
The most important point first: what's licensed for weight loss
In the UK, medicines are only prescribed for the uses they are licensed for. Ozempic contains semaglutide and is licensed for type 2 diabetes. The weight-management version of semaglutide is a separate product: Wegovy.
So when people compare "Mounjaro vs Ozempic" for weight loss, the fairer, more accurate comparison for a UK reader is Mounjaro (tirzepatide) versus Wegovy (semaglutide) — the two treatments licensed here specifically for weight management. This article explains the science behind both active ingredients so the differences make sense.
How each medicine works
Semaglutide (the active ingredient in both Ozempic and Wegovy) is a GLP-1 receptor agonist. It mimics a natural gut hormone that controls appetite: you feel fuller sooner and for longer, and the stomach empties more slowly.
Tirzepatide (Mounjaro) goes a step further. It activates two gut-hormone receptors at once — GLP-1 and GIP. The idea is that engaging both pathways may support appetite regulation and blood-sugar control together.
Both are given as a weekly self-injection, and both are gradually titrated upwards to help your body adjust and to reduce side effects.
Doses side by side
Both medicines start low and step up over several weeks. A prescriber decides each increase.
| Medicine | Starting dose | Titration steps | Maximum licensed dose |
|---|---|---|---|
| Mounjaro (tirzepatide) | 2.5mg weekly | 2.5 → 5 → 7.5 → 10 → 12.5 → 15mg | 15mg weekly |
| Wegovy (semaglutide) | 0.25mg weekly | 0.25 → 0.5 → 1 → 1.7 → 2.4 → 7.2mg | 7.2mg weekly |
You do not choose your own dose. Escalation depends on how you respond and tolerate treatment, and is reviewed by a GPhC-registered prescriber at each step.
What the trials showed
Each medicine has been studied in large clinical trials. These are separate trials, run at different times, so the figures below are not a head-to-head comparison — you cannot simply subtract one from the other.
- Mounjaro: In the SURMOUNT-1 trial, participants on the 15mg dose lost on average 22.5% of body weight over 72 weeks, alongside lifestyle support. Individual results vary; not everyone reaches this.
- Wegovy: In the STEP UP clinical trial, adults on the 7.2mg dose lost on average 20.7% of their body weight over 72 weeks, alongside lifestyle support. Individual results vary; not everyone reaches this.
Both trials pair the medicine with diet, activity and behavioural support — the medicine is a tool, not a replacement for those changes.
Side effects: a shared profile
Because both are GLP-1 based, they share a similar side-effect profile. The most common effects (affecting more than 1 in 10 people) are digestive and often ease as your body adjusts:
- Nausea
- Diarrhoea
- Constipation
- Vomiting
- Decreased appetite
- Fatigue
Serious but rare risks for both include severe allergic reaction, acute pancreatitis, severe hypoglycaemia (particularly relevant with certain diabetes medicines), severe gastrointestinal disease and worsening diabetic retinopathy.
If you experience side effects, you can report them through the MHRA Yellow Card scheme at https://yellowcard.mhra.gov.uk/.
Cost compared
Prices depend on the medicine and the dose you reach. At The Weight Clinic, both start from £115/month.
| Dose | Mounjaro | Dose | Wegovy |
|---|---|---|---|
| 2.5mg | £160 | 0.25mg | £115 |
| 5mg | £185 | 0.5mg | £125 |
| 7.5mg | £240 | 1mg | £135 |
| 10mg | £260 | 1.7mg | £175 |
| 12.5mg | £275 | 2.4mg | £230 |
| 15mg | £295 | 7.2mg | £245 |
The online consultation is free — you only pay if a treatment is prescribed and you choose to proceed.
Prefer a tablet instead of an injection?
If needles are a concern, there are now oral options for the same active medicine. The Wegovy Tablet is oral semaglutide, taken once daily on an empty stomach with a small sip of plain water, then waiting at least 30 minutes before eating, drinking anything else or taking other medicines — taken with food it is far less effective.
A newer small-molecule GLP-1 tablet, Foundayo (orforglipron), can be taken at any time of day with or without food or water. You can explore all of these on our treatments overview or the combined weight-loss injections page.
Which might suit you?
There is no single "best" medicine — the right choice depends on your health history, other medicines, how you tolerate treatment and your preferences. Both share the same core eligibility:
- Aged 18 or over.
- BMI of 30 or above, or BMI 27–30 with a weight-related condition such as type 2 diabetes, high blood pressure or sleep apnoea.
Neither is suitable if you are pregnant, planning pregnancy or breastfeeding, have type 1 diabetes, a personal or family history of medullary thyroid carcinoma or MEN2, a history of pancreatitis, severe gastrointestinal disease, an active eating disorder, severe liver or kidney impairment, or a known allergy to the active ingredient.
A registered independent prescriber decides what is clinically appropriate for you. Treatment is never guaranteed. You can begin with a free online consultation to check your eligibility, and read more about The Weight Clinic and our regulated process.
This article is for information only and is not a substitute for personalised medical advice. Weight-loss medicines are prescription-only, are not suitable for everyone, and are prescribed only after a clinical consultation with a GPhC-registered prescriber. Individual results vary. Always speak to a UK-registered pharmacist or doctor before starting or changing any prescription medication.
