Mounjaro (tirzepatide) has rapidly become one of the most sought-after weight-loss treatments in the UK. Whether you are just starting to research it or ready to begin treatment, this comprehensive guide covers everything you need to know as of late 2025.
What Is Mounjaro?
Mounjaro is a prescription injectable medication manufactured by Eli Lilly. Its active ingredient, tirzepatide, is a dual GIP/GLP-1 receptor agonist—the first of its kind. By targeting two incretin hormone pathways simultaneously, it delivers more potent appetite suppression and metabolic benefits than single-receptor drugs like semaglutide.
How Effective Is It?
In the landmark SURMOUNT-1 trial, participants taking the highest dose (15 mg) lost an average of 22.5% of their body weight over 72 weeks. This is the highest average weight loss recorded for any approved anti-obesity medication to date.
Who Is Eligible in the UK?
- Adults aged 18 and over.
- BMI of 30+ (or 27+ with at least one weight-related comorbidity such as type 2 diabetes, hypertension or sleep apnoea).
- Commitment to dietary changes and increased physical activity alongside medication.
NICE approved Mounjaro for weight management in eligible adults, and NHS availability is gradually expanding across England, Scotland, Wales and Northern Ireland.
Dosing and Titration
Mounjaro is injected once weekly using a pre-filled KwikPen. The standard titration schedule is:
- Weeks 1–4: 2.5 mg
- Weeks 5–8: 5 mg
- Week 9 onwards: increases of 2.5 mg every 4 weeks, up to a maximum of 15 mg
Your prescriber will determine your optimal maintenance dose based on tolerability and response.
Common Side Effects
The most frequently reported side effects are gastrointestinal: nausea, diarrhoea, constipation, vomiting and reduced appetite. These are usually most pronounced during the first four weeks and at each dose increase. Serious but rare risks include pancreatitis and gallbladder disease.
Cost in the UK
Private Mounjaro prescriptions typically cost between £150 and £300 per month, depending on your dose and chosen pharmacy. Prices can vary by as much as £50–£100 between pharmacies for the same dose, making price comparison essential. MedsLens helps you find the lowest price from GPhC-registered pharmacies in seconds.
How to Get Mounjaro
- NHS: Through specialist weight-management services where available. Referral from your GP is usually required.
- Private prescription: Via online pharmacies registered with the GPhC, following an online consultation with a prescriber.
Storage and Handling
Store unused pens in the fridge at 2–8°C. Once in use, a pen can be kept at room temperature (below 30°C) for up to 21 days. Dispose of used pens in a sharps bin and return full bins to your local pharmacy or council.
Looking Ahead
Research into tirzepatide continues, with studies exploring its effects on heart failure, sleep apnoea and non-alcoholic fatty liver disease. As the evidence base grows and NHS access expands, Mounjaro is set to play an increasingly central role in UK obesity treatment throughout 2025 and beyond.