Mounjaro in the UK:
Tirzepatide Guide

What is Mounjaro?

Mounjaro is the brand name for tirzepatide, a novel once-weekly injectable medication manufactured by Eli Lilly. Unlike Ozempic and Wegovy, which act solely on the GLP-1 receptor, Mounjaro is a dual-action medicine that targets both the glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptors simultaneously.

This dual mechanism of action sets tirzepatide apart from other incretin-based therapies. By activating both receptor pathways, Mounjaro enhances insulin secretion, improves insulin sensitivity, reduces glucagon levels, slows gastric emptying and modulates appetite through complementary pathways in the brain. Clinical trials have consistently demonstrated that this combined approach produces greater improvements in both glycaemic control and body weight compared with GLP-1 receptor agonists alone.

Tirzepatide received MHRA marketing authorisation in the UK for the treatment of type 2 diabetes and has subsequently been appraised by NICE for weight management, making it available through the NHS for both indications.

NHS availability and NICE guidance

Mounjaro is available on the NHS for two distinct indications, each covered by separate NICE guidance.

For type 2 diabetes

NICE has recommended tirzepatide as an option for treating type 2 diabetes in adults when diet, exercise and existing glucose-lowering therapies have not achieved adequate glycaemic control. The prescribing criteria are broadly similar to those for other GLP-1 receptor agonists, including:

• HbA1c above target despite optimised treatment with metformin and at least one other oral agent
• BMI of 35 or above (adjusted for ethnicity), or BMI below 35 where insulin therapy would otherwise be initiated and there are occupational or clinical concerns about hypoglycaemia

For weight management

NICE has also appraised tirzepatide for chronic weight management in adults meeting the following criteria:

• BMI of 35 or above, or BMI of 30 to 34.9 with at least one weight-related comorbidity
• Management within a specialist weight management service (Tier 3 or equivalent)
• Participation in a structured behavioural programme
• Adjusted BMI thresholds for certain ethnic groups

Private prescription costs

For patients seeking private access to Mounjaro, costs vary depending on the dose level and provider. Tirzepatide is available through many of the same digital health platforms and pharmacies that supply semaglutide products.

Dosage schedule

Mounjaro follows a stepwise dose-escalation protocol. The starting dose is 2.5 mg once weekly for 4 weeks, increasing in 2.5 mg increments at minimum 4-week intervals:

1. Weeks 1–4: 2.5 mg weekly (initiation, not therapeutic)
2. Weeks 5–8: 5 mg weekly (first potential maintenance dose)
3. Further escalation: 7.5 mg, 10 mg, 12.5 mg and 15 mg available at 4-week intervals if clinically indicated

The maintenance dose is individualised based on clinical response and tolerability. Not all patients will need to escalate to the maximum 15 mg dose. Many achieve satisfactory outcomes at 5 mg or 10 mg.

Clinical evidence: how effective is Mounjaro?

The SURPASS and SURMOUNT clinical trial programmes provide the evidence base for Mounjaro. These large-scale studies have established tirzepatide as the most effective injectable weight loss medication studied to date.

Key results

• SURMOUNT-1 (weight management): Average weight loss of 20.9 per cent with the 15 mg dose at 72 weeks, versus 3.1 per cent with placebo. Approximately one-third of participants lost more than 25 per cent of their body weight.
• SURMOUNT-2 (type 2 diabetes + obesity): Average weight loss of 14.7 per cent with the 15 mg dose at 72 weeks
• SURPASS-2 (head-to-head vs semaglutide 1 mg): Tirzepatide 15 mg produced significantly greater HbA1c reduction and weight loss compared with semaglutide 1 mg
• SURPASS-3 (vs insulin degludec): Superior glycaemic control and weight loss compared with insulin therapy

Mounjaro vs semaglutide: how do they compare?

Mounjaro and semaglutide-based products (Ozempic, Wegovy) represent the two principal GLP-1-based treatment options available in the UK. Their differences extend beyond the active ingredient.

For a full three-way comparison, see our UK weight loss injections comparison.

Side effects

Mounjaro shares many side effects with other GLP-1-based treatments, primarily affecting the gastrointestinal system. These tend to be most prominent during dose escalation and usually diminish with time.

Common side effects

• Nausea (most frequently reported)
• Diarrhoea
• Vomiting
• Constipation
• Decreased appetite
• Abdominal pain or discomfort
• Injection site reactions

Less common but serious side effects

• Pancreatitis
• Gallbladder disease
• Hypoglycaemia (especially when combined with insulin or sulphonylureas)
• Allergic reactions

For comprehensive information about managing side effects, visit our GLP-1 side effects guide.

Who should not take Mounjaro?

• People with a personal or family history of medullary thyroid carcinoma or MEN 2
• Known hypersensitivity to tirzepatide or any excipients
• Pregnant or breastfeeding women
• People with type 1 diabetes or diabetic ketoacidosis

Frequently asked questions

Is Mounjaro better than Ozempic?

Head-to-head clinical trial data (SURPASS-2) showed that tirzepatide produced greater reductions in HbA1c and body weight compared with semaglutide 1 mg. However, no direct comparison with the higher semaglutide doses used in Wegovy (2.4 mg) has been completed. The choice between Mounjaro and semaglutide depends on your individual clinical circumstances, treatment goals and prescriber recommendation.

Can my GP prescribe Mounjaro?

Yes, GPs can prescribe Mounjaro for type 2 diabetes in line with NICE guidance. For weight management, initiation typically occurs through specialist weight management services, although ongoing prescribing may be transferred to primary care through shared care arrangements.

How long does Mounjaro take to work?

Blood sugar improvements are usually observed within 2 to 4 weeks. Meaningful weight loss typically begins during the first month and continues progressively over the following 12 to 18 months as doses are escalated.