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Tirzepatide

Dual GIP and GLP-1 receptor agonist · Mounjaro

UK status

MHRA licensed

Availability

Prescription only

Evidence base

Human RCT, phase 3

Controlled drug

No

Tirzepatide does what semaglutide does, and one more thing on top. It was the first drug approved anywhere in the world to target two incretin hormone receptors together, which is the main reason it gets compared favourably to what came before it.

01What it is

Your gut releases more than one hormone after eating. GLP-1 is one. GIP, glucose-dependent insulinotropic polypeptide, is another, and it was less well understood as a drug target for a long time.

Tirzepatide is a single molecule engineered to activate both receptors. It is a 39-amino-acid peptide with a fatty acid chain attached, which is what gives it a once-weekly duration in the same way semaglutide gets one.

02UK legal and licensing status

Tirzepatide holds two separate UK authorisations. The MHRA licensed it for type 2 diabetes in 2022, and for weight management in adults in November 2023. It is marketed as Mounjaro.

Access on the NHS is a separate question from licensing, and it is where most of the public confusion sits. NICE guidance TA1026 covers tirzepatide for weight management, and it sets eligibility criteria rather than making it generally available. NHS England has run a phased rollout, initially through specialist weight management services, with prescribing in general practice arriving later and varying by area.

Eligibility criteria and rollout arrangements change. Check the current NICE guidance and your local ICB position rather than relying on any summary, including this one.

03How it works

Tirzepatide activates the GLP-1 receptor, producing the same three effects described on the semaglutide record, and it also activates the GIP receptor.

• GLP-1 receptor. Glucose-dependent insulin release, slower gastric emptying, reduced appetite signalling.
• GIP receptor. Also increases insulin release after eating, and appears to act on fat tissue and on appetite regulation in ways that are still being characterised.
• Why the combination matters. The working theory is that hitting both receptors produces a larger metabolic effect than either alone. How much of the observed difference comes from GIP specifically is still an open research question.

04What the evidence shows

The evidence base is the SURPASS programme for type 2 diabetes and the SURMOUNT programme for weight management, both funded by Eli Lilly. These are large, randomised, phase 3 trials.

05Reported harms

Gastrointestinal effects are the most commonly reported, typically described as mild to moderate and easing with continued use. The MHRA classifies tirzepatide as a black triangle medicine, meaning it is under additional safety monitoring and all suspected adverse reactions should be reported through the Yellow Card scheme.

The contraception and surgery points on the semaglutide record apply here too. NHS England specifically advises additional contraception alongside the pill, and considering patches or gels rather than tablets for HRT.

The MHRA issued an alert in February 2026 about falsified Mounjaro pens. Product from social media sellers, messaging apps or any source other than a registered pharmacy cannot be verified.

06Sources

Links go to the primary source. Where a source is behind a paywall or requires registration, the citation is given so you can find it yourself.

1. Summary of Product Characteristicselectronic medicines compendium
2. Tirzepatide monographBNF
3. TA1026, tirzepatide for managing overweight and obesityNICE
4. Interim commissioning guidance for TA1026NHS England
5. Weight loss medicines in EnglandHouse of Commons Library briefing
6. SURMOUNT 1 trialNew England Journal of Medicine, 2022
7. Falsified Mounjaro pens alertMHRA, February 2026