Mounjaro vs Ozempic: What’s the Difference and What Should You Know in 2025?
With the rise of weight-loss medications, Mounjaro and Ozempic have become household names.
But what sets them apart, and how accessible are they in the UK?
Here’s what you need to know.
How They Work
- Ozempic (semaglutide) is a GLP-1 receptor agonist, which mimics a hormone that helps regulate blood sugar, slows digestion, and reduces appetite [1].
- Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormones involved in insulin secretion and appetite regulation. This dual action makes it more effective for weight loss in clinical trials so far [2].
Key Differences
| Feature | Ozempic | Mounjaro |
|---|---|---|
| Active Ingredient | Semaglutide | Tirzepatide |
| Mechanism | GLP-1 agonist | Dual GIP + GLP-1 agonist |
| Weight Loss (avg.) | ~13 lbs (5.9 kg) | ~17–25 lbs (7.7–11.4 kg) – think of this as around 20% weight loss |
| Dosing | Weekly injection (up to 2 mg) | Weekly injection (up to 2 mg) |
Common Side Effects
Both medications share similar side effects, including:
- Nausea
- Diarrhoea or constipation
- Abdominal discomfort
- Fatigue
- Headache
These are typically more pronounced at the start of treatment and may lessen over time[1].
Common Myths
- “They’re just for diabetics.”
While originally developed for type 2 diabetes, both are now widely prescribed off-label for weight loss, especially in cases of obesity. - “You’ll regain all the weight if you stop.”
Weight regain is possible, but not inevitable. Long-term lifestyle changes are key to maintaining results. - “They’re dangerous”
These are longstanding and very safe drugs with a large evidence base. They are, however, still potentially serious medication and so we would want it to be for the right patient, in the right situation, at the right time and with the right follow up. At Stonegate Medical Clinic we don’t cut corners to lose weight.
This is EXACTLY the reason we do not advise buying your weight loss medication off websites with no proper care or follow up.
Impact on Contraception and HRT
- There’s no direct evidence that either drug reduces the effectiveness of hormonal contraception or HRT but some cases have been reported in the media.
- Severe gastrointestinal side effects (like vomiting or diarrhoea) could theoretically reduce absorption of oral contraceptives and there could also be delayed emptying of your stomach contents – this may also impact the effectiveness of your contraception / HRT.
- At Stonegate Medical Clinic we would look at this with you as an individual but often advise adding barrier methods of contraception till you are settled on a dose, or switching you to non tablet form Contraception / HRT if that suited better.
Can You Get Them on the NHS?
Under current NICE guidelines, access to these medications for weight loss is highly restricted:
- Ozempic is not approved for weight loss on the NHS. It is only prescribed for type 2 diabetes.
- Wegovy (a higher-dose semaglutide) is approved for weight loss but only under strict criteria:
- BMI ≥35 (or ≥30 with comorbidities)
- Must be prescribed through a specialist weight management service
- Maximum treatment duration: 2 years
- Mounjaro is not yet approved by NICE for weight loss, though it may be prescribed privately or off-label for diabetes.
This means that for most people seeking weight loss support, private prescriptions are currently the only route to access Mounjaro or Ozempic for this purpose.
Final Thoughts
Both Mounjaro and Ozempic offer powerful tools for managing weight and blood sugar. They are very safe but are serious medications and so should be done under medical supervision and ideally not from an online provider with no accountability – weight is just part of ensuring your health is optimal.
Mounjaro may offer greater weight loss due to its dual-action mechanism. This is the medication we advise at Stonegate Medical Clinic.
References
[1] Mounjaro vs Ozempic: Which is right for you? – Drugs.com