Mounjaro (Tirzepatide) for Weight Loss: What UK Patients Need to Know

What is Mounjaro?

Mounjaro is the brand name for tirzepatide, a once-weekly injectable medicine licensed in the UK for the management of type 2 diabetes and, more recently, for chronic weight management in adults with obesity or overweight with weight-related health conditions. It is manufactured by Eli Lilly and was approved by the MHRA for weight management in the UK in 2023.

How does tirzepatide work?

Tirzepatide is described as a dual agonist — it activates two receptors simultaneously: the GLP-1 (glucagon-like peptide-1) receptor and the GIP (glucose-dependent insulinotropic polypeptide) receptor. Both GLP-1 and GIP are naturally occurring gut hormones released after eating. By activating both receptors, tirzepatide produces a more pronounced effect on appetite suppression, calorie intake, and metabolic function than medicines that act on GLP-1 alone.

The key effects include:

• Significantly reduced appetite and food cravings
• Slowed gastric emptying, increasing the feeling of fullness after meals
• Improved insulin sensitivity and blood glucose regulation
• Reduced fat storage, particularly visceral fat

What do the clinical trials show?

The SURMOUNT clinical trial programme provides the most comprehensive evidence for tirzepatide in weight management:

• SURMOUNT-1 — In adults with obesity or overweight without diabetes, participants taking the highest dose (15 mg) achieved an average weight loss of 22.5% of body weight over 72 weeks. Over a third of participants lost 25% or more of their body weight.
• SURMOUNT-2 — In adults with type 2 diabetes, average weight loss was 15.7% at the highest dose — substantially greater than any previously approved medicine for this population.
• SURMOUNT-4 — Participants who lost weight on tirzepatide and then continued treatment maintained their weight loss, while those switched to placebo regained approximately two-thirds of the weight lost.

What are the available doses?

Tirzepatide is started at a low dose and increased gradually to minimise side effects. The dose escalation schedule typically follows this pattern: 2.5 mg for four weeks, then 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg — each dose held for at least four weeks before escalating. Not everyone needs to reach the maximum dose; the target dose is the highest that is well tolerated and producing the desired effect.

What are the common side effects?

The most common side effects are gastrointestinal and include nausea, vomiting, diarrhoea, constipation, and reduced appetite. These are most pronounced when starting treatment or increasing the dose, and typically improve over time. Starting at a low dose and escalating slowly is the most effective way to minimise these effects. Serious side effects are uncommon but include pancreatitis, gallbladder problems, and — in those with a relevant personal or family history — thyroid tumours.

Is Mounjaro available on the NHS?

As of 2026, tirzepatide is available through NHS specialist weight management services in England for eligible patients, subject to local commissioning decisions. Access through NHS primary care remains limited. Many patients access tirzepatide through regulated private medical weight loss services while NHS provision expands.

Book a consultation with Weight Loss Wales to discuss whether tirzepatide is appropriate for you.