Mounjaro (tirzepatide) UK research guide 2026

What is Mounjaro?

Mounjaro is Eli Lilly's proprietary brand of tirzepatide, a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist. It was granted MHRA marketing authorisation in November 2023 for the management of type 2 diabetes mellitus in adults, with a second indication for chronic weight management in adults added in 2024. Mounjaro is supplied as a prefilled KwikPen autoinjector available in six dose strengths, from the 2.5 mg starting dose through to the 15 mg maintenance dose.

UK regulatory status

Mounjaro holds a full MHRA licence for two indications: type 2 diabetes (in combination with diet and exercise, with or without other glucose-lowering agents) and chronic weight management in adults with a body mass index of 30 kg/m² or above, or 27 kg/m² or above in the presence of at least one weight-related comorbidity. NICE technology appraisal TA1026 (2024) recommended Mounjaro for NHS use in England within specialist weight-management services, subject to eligibility criteria. Private prescription via licensed UK clinicians is available outside the NHS pathway. Supply has remained broadly stable since launch; no sustained national shortages equivalent to those experienced with Wegovy and Ozempic between 2022 and 2024 have been recorded for Mounjaro in the UK market.

Clinical evidence summary

The SURPASS programme (SURPASS-1 through 5) established tirzepatide's glycaemic efficacy in type 2 diabetes. SURPASS-1 (monotherapy) demonstrated HbA1c reductions of 1.87–2.07% and weight reductions of 7–9.5 kg at 40 weeks across the 5, 10, and 15 mg doses. SURPASS-2 compared tirzepatide directly to semaglutide 1 mg (Ozempic), showing superior HbA1c and weight reduction at all doses. SURPASS-5 demonstrated efficacy in combination with basal insulin, a combination frequently encountered in clinical practice.

The SURMOUNT programme addressed obesity specifically. SURMOUNT-1 (n = 2,539 adults without diabetes) showed mean weight reductions of 15.0%, 19.5%, and 20.9% at 72 weeks for the 5, 10, and 15 mg doses respectively versus 3.1% for placebo. SURMOUNT-2 (participants with type 2 diabetes) demonstrated mean weight reductions of approximately 13.4–15.7% at 72 weeks. SURMOUNT-3 and SURMOUNT-4 examined intensive lifestyle run-in and maintenance, respectively, confirming that weight regain on withdrawal is substantial. SURMOUNT-5, a head-to-head comparison with semaglutide 2.4 mg, reported a 47% greater relative weight reduction with tirzepatide 10 and 15 mg at 72 weeks.

Mechanism

Tirzepatide acts as a balanced co-agonist at both GIP and GLP-1 receptors via a single synthetic peptide backbone with a C20 fatty-diacid side chain that confers tight albumin binding and a half-life of approximately five days. GLP-1 agonism drives gastric emptying delay, satiety signalling, and glucose-dependent insulin secretion; GIP agonism contributes to adipocyte biology and may potentiate GLP-1-mediated satiety. For the full mechanistic profile, see the tirzepatide molecule page.

Dosing and administration

Mounjaro is administered as a subcutaneous injection once weekly, at any time of day irrespective of meals. The titration schedule starts at 2.5 mg weekly for the first four weeks; the dose is then increased in 2.5 mg steps every four weeks: 2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg. Maintenance dose (the highest tolerated between 5 and 15 mg) is continued long term. Dose escalation may be deferred by four additional weeks at any step if gastrointestinal side effects are problematic. Injection sites include the abdomen, thigh, or upper arm; sites should be rotated.

Common side effects

The side-effect profile of Mounjaro is typical of the incretin class. In SURMOUNT-1, the most frequent adverse events leading to discontinuation were gastrointestinal in nature: nausea (affecting approximately 31–44% of participants on active treatment), diarrhoea (17–22%), vomiting (8–13%), and constipation (11–14%). Decreased appetite is common and is central to the mechanism of weight reduction. Effects are dose-dependent and most pronounced during dose escalation; the majority of patients develop tolerance over four to eight weeks at any given dose level. The overall discontinuation rate due to adverse events in SURMOUNT-1 was 4.3–7.4% across active arms.

Mounjaro vs alternative brands

The table below compares Mounjaro with the principal alternative licensed for weight management in the UK, Wegovy, alongside Ozempic and Saxenda for broader context.

See also: Wegovy brand guide · Ozempic brand guide · Zepbound brand guide (the US brand of the same tirzepatide molecule) · Tirzepatide vs Retatrutide.

Procurement and supplier position

This page is educational and does not advertise, sell, supply, recommend or rank any supplier, compounder, online pharmacy or telehealth service for Mounjaro or any version of tirzepatide. Mounjaro is a UK prescription-only medicine and should only be accessed through a qualified UK prescriber following appropriate clinical assessment. Compounded or grey-market "tirzepatide" is not the same regulated product as Mounjaro; the MHRA has warned about compounded weight-loss injectables, and the risks of counterfeit pens are discussed on our counterfeit weight-loss pens page.

Frequently asked questions

Is Mounjaro available on the NHS?

Mounjaro (tirzepatide) received NICE approval for use in NHS England specialist weight-management services in 2024. Eligibility criteria apply: a BMI ≥35 with at least one weight-related comorbidity, or lower BMI thresholds in certain ethnic groups. Prescribing is via Tier 3 or Tier 4 specialist services, not general practice at present.

What is the difference between Mounjaro and Wegovy?

Both are licensed for chronic weight management in the UK, but they contain different molecules. Mounjaro contains tirzepatide, a dual GIP/GLP-1 receptor agonist manufactured by Eli Lilly. Wegovy contains semaglutide 2.4 mg, a selective GLP-1 agonist from Novo Nordisk. Head-to-head trial data (SURMOUNT-5, 2024) demonstrated greater mean weight reduction with tirzepatide at 72 weeks.

Is Mounjaro the same as Zepbound?

Yes — both contain tirzepatide manufactured by Eli Lilly. Mounjaro is the UK (and EU) brand name; Zepbound is the US brand name for the weight-management indication. The molecule, dosing schedule, and prefilled pen device are essentially identical, though the pens differ in minor device design.

What does Mounjaro actually contain?

Each Mounjaro prefilled KwikPen contains tirzepatide — a 39-amino-acid synthetic peptide with dual agonist activity at the GIP and GLP-1 receptors. It also contains a fatty-diacid moiety attached via a linker to enable albumin binding, extending its half-life to approximately five days and enabling once-weekly dosing.

How long does Mounjaro titration take?

The licensed titration schedule begins at 2.5 mg weekly and increases in 2.5 mg increments every four weeks: 2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg. Full maintenance dose (15 mg) is typically reached at approximately 20–24 weeks. Dose escalation may be slowed if gastrointestinal tolerability is a concern.

Can Mounjaro be used for type 2 diabetes as well as weight loss?

Yes. Mounjaro is MHRA-licensed for both type 2 diabetes management (since November 2023) and chronic weight management (indication added in 2024). For diabetes, it is prescribed alongside diet and exercise and may be used in combination with metformin, SGLT-2 inhibitors, or basal insulin.