We have compiled the most frequently asked questions from UK Mounjaro users and answered each one based on current clinical evidence and prescribing guidance.
Getting Started
1. How quickly does Mounjaro work? Most people notice reduced appetite within the first week. Visible weight loss typically begins within two to four weeks.
2. What is the starting dose? All patients start on 2.5 mg once weekly, regardless of body weight.
3. Do I need a prescription? Yes. Mounjaro is a prescription-only medicine (POM) in the UK. You need a consultation with a prescriber, either face-to-face or via an online pharmacy.
4. Can my GP prescribe it? Some GPs can prescribe Mounjaro, but as of late 2025, most UK patients obtain it through specialist weight-management services or licensed online pharmacies.
Using Mounjaro
5. Does the injection hurt? The needle is very fine. Most users describe a brief pinch or feel nothing at all.
6. What time of day should I inject? There is no required time. Choose whatever time is most convenient and consistent for you.
7. What if I miss a dose? If fewer than 4 days have passed, take it as soon as you remember. If more than 4 days, skip that dose and take the next one on your regular day.
8. Can I inject into my stomach? Yes. The abdomen, thigh and upper arm are all approved sites. Rotate between them.
Side Effects
9. What are the most common side effects? Nausea, diarrhoea, constipation, reduced appetite and injection-site reactions.
10. How long does nausea last? Usually one to three days after each injection, improving as your body adjusts. It is typically worst during the first four weeks.
11. Does Mounjaro cause hair loss? Some users experience temporary hair shedding (telogen effluvium) due to rapid weight loss, not the drug directly.
Lifestyle
12. Can I drink alcohol on Mounjaro? Alcohol is not contraindicated, but it may worsen nausea and adds empty calories. Moderation is strongly advised.
13. Can I exercise normally? Yes, and exercise is encouraged. Resistance training helps preserve muscle mass during weight loss.
14. Do I need to follow a specific diet? No specific diet is required, but a high-protein, balanced diet maximises results and minimises muscle loss.
Results
15. How much weight will I lose? Clinical trials showed average losses of 15–22% of body weight over 72 weeks, but individual results vary.
16. Will I regain weight if I stop? Studies show that weight regain is common after stopping any weight-loss medication. Long-term use or a structured maintenance plan is recommended.
17. Does Mounjaro work for everyone? Most people respond, but about 10–15% of trial participants did not achieve clinically significant weight loss. Non-responders should discuss alternatives with their prescriber.
Practical Matters
18. How much does it cost? Between £150 and £300 per month in the UK, depending on dose and pharmacy. Use MedsLens to compare prices.
19. How should I store it? Unused pens in the fridge at 2–8°C. An in-use pen can be kept at room temperature (up to 30°C) for up to 21 days.
20. Is it available on the NHS? NICE has approved Mounjaro for weight management in eligible adults. Availability through NHS services is expanding but may vary by region.