Tirzepatide

Key points

• Tirzepatide activates two gut hormone receptors, GIP and GLP-1, to lower appetite and blood sugar.
• It is licensed in the UK as Mounjaro, for weight management and for type 2 diabetes.
• It is a prescription only medicine, so a registered prescriber must assess you first.
• It is given as a once weekly injection under the skin, with the dose raised in steps.
• NICE recommends it for weight management on the NHS for some people, with access rolling out in stages. It is also available privately through registered providers.

Quick facts

UK status

Licensed prescription only medicine

Licensed as

Mounjaro (weight management and type 2 diabetes)

Class

GIP and GLP-1 receptor agonist

Half life

About 5 days, so it is given once weekly

Given as

Once weekly injection under the skin

Legal supply

NHS services, CQC registered clinics, GPhC registered pharmacies

Dosing: the licensed step up

Mounjaro is started low and raised in steps, usually every 4 weeks, to reduce stomach side effects. Maintenance is 5 mg, 10 mg or 15 mg once weekly, depending on response and tolerance. The schedule below is the licensed step up.

This is the licensed schedule, not a dosing recommendation. Your prescriber sets your dose and may move more slowly if you have side effects. Never change the dose yourself.

Put your own dates on it: Mounjaro dose schedule →

How it works

Tirzepatide copies two hormones the gut releases after eating, GIP and GLP-1. Acting on both receptors reduces appetite, slows how quickly the stomach empties, and improves how the body handles blood sugar. Working on two pathways is why it is often more effective than medicines that act on GLP-1 alone.

What the evidence shows

Tirzepatide has been studied in the SURMOUNT trials for weight management and the SURPASS trials for type 2 diabetes. In SURMOUNT 1, average weight loss reached around 20% of body weight at the highest dose over about 72 weeks. In a head to head diabetes trial it lowered blood sugar and weight more than semaglutide.

What it does not settle

• How much weight people keep off after stopping. As with other GLP-1 medicines, much of it tends to return.
• Safety over many years is still being followed up.
• Results vary between individuals, and trials pair the medicine with diet and activity support.

Side effects

Common

• Nausea, vomiting, diarrhoea and constipation, most often while the dose is going up. These usually ease with time.
• Reduced appetite, tiredness and stomach discomfort.

Less common but serious

• Pancreatitis is rare but serious. Seek urgent medical help for severe, lasting stomach pain, especially with vomiting.
• Gallbladder problems, and low blood sugar when combined with certain diabetes medicines.

Report any suspected side effect through the MHRA Yellow Card scheme.

UK legal status and access

Tirzepatide is a licensed prescription only medicine, so there is a legal, regulated supply in the UK. NICE recommends Mounjaro for weight management on the NHS for people who meet its criteria, and access is being phased in. You can also be seen privately through a CQC registered clinic or a GPhC registered pharmacy. Buying it without an assessment, or from an unregistered seller, risks a fake or unsafe product.

UK approvals

• Dec 2024NICE recommended tirzepatide (Mounjaro) for managing overweight and obesity in people who meet its criteria.
• Jun 2025Access for weight loss began to reach patients through NHS primary care, as part of a phased rollout.

Common questions