Zepbound (tirzepatide) UK research guide 2026

What is Zepbound?

Zepbound is Eli Lilly's US brand name for tirzepatide when prescribed for chronic weight management. It received FDA approval in November 2023 for adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related comorbidity. Critically, Zepbound is not licensed or marketed in the United Kingdom. The UK equivalent — tirzepatide for the same indication — is marketed by the same manufacturer, Eli Lilly, under the brand name Mounjaro. The active molecule, dosing schedule, and clinical evidence base are identical; the distinction is purely one of brand naming and regulatory filing strategy.

UK regulatory status

Zepbound holds no MHRA marketing authorisation. It is a US-licensed product and has not been submitted for approval under that brand name in the UK or EU. Eli Lilly's regulatory strategy for tirzepatide in the UK uses a single brand — Mounjaro — for both the type 2 diabetes and weight-management indications. Patients in the UK seeking tirzepatide for weight management should be prescribed Mounjaro through a licensed UK clinician, not seek to obtain Zepbound from the United States. Importation of prescription medicines without appropriate authorisation raises significant regulatory and patient-safety concerns and is not recommended. UK researchers investigating tirzepatide as a compound should note that all UK clinical and regulatory data is filed under the Mounjaro brand.

Clinical evidence summary

Zepbound's FDA approval was grounded in the SURMOUNT clinical programme — specifically SURMOUNT-1 and SURMOUNT-2 — which are the same trials that underpin Mounjaro's weight-management licence in the UK. SURMOUNT-1 (n = 2,539 adults with obesity or overweight without diabetes) demonstrated 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. Approximately 89.5% of participants receiving 15 mg achieved at least 5% weight reduction. SURMOUNT-2 demonstrated 13.4–15.7% weight reduction in adults with concurrent type 2 diabetes. SURMOUNT-3 and SURMOUNT-4 confirmed that weight regain follows treatment withdrawal. SURMOUNT-5, comparing tirzepatide directly with semaglutide 2.4 mg (Wegovy), reported a 47% greater relative weight reduction with tirzepatide. The SURPASS programme (1–5) provides the diabetes evidence base for the same molecule.

Mechanism

Tirzepatide, the active molecule in Zepbound, is a dual GIP/GLP-1 receptor agonist. Its 39-amino-acid backbone mimics both incretin hormones simultaneously via a single peptide, with a fatty-diacid moiety that confers albumin binding and a half-life of approximately five days. For the full mechanistic profile, see the tirzepatide molecule page.

Dosing and administration

The dosing schedule for Zepbound in the US is identical to Mounjaro in the UK: a 2.5 mg weekly starting dose titrated every four weeks through 5, 7.5, 10, 12.5, and 15 mg to a maintenance dose of 10 or 15 mg weekly. In the US, Zepbound is also available in single-dose vials intended for self-injection, in addition to prefilled autoinjector pens. Administration is subcutaneous into the abdomen, thigh, or upper arm.

Common side effects

The side-effect profile is identical to Mounjaro, as the molecule and doses are the same. Gastrointestinal effects — nausea, diarrhoea, vomiting, and constipation — are the most common, occurring in approximately 30–44% of patients for nausea, predominantly during dose escalation. Discontinuation rates due to adverse events were approximately 4.3–7.4% across active arms in SURMOUNT-1. Effects are dose-dependent and generally diminish once steady-state at a given dose is reached.

Zepbound vs Mounjaro: a UK perspective

For UK researchers and clinicians, the comparison between Zepbound and Mounjaro is largely a regulatory and nomenclature question rather than a pharmacological one.

See also: Mounjaro brand guide · Wegovy brand guide · 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 Zepbound, Mounjaro or any version of tirzepatide. Zepbound is a US-licensed prescription medicine and is not the same regulated product as UK-licensed Mounjaro, even though the active ingredient is identical. UK access to tirzepatide for weight management is via Mounjaro through a qualified UK prescriber following appropriate clinical assessment. See UK POM context for GLP-1 medicines.

Frequently asked questions

Is Zepbound available in the UK?

Zepbound is not licensed or marketed in the UK. The UK equivalent — tirzepatide for weight management — is branded and sold as Mounjaro by Eli Lilly. Both contain the identical active molecule at identical doses; the difference is purely a brand-naming decision by Eli Lilly to differentiate the diabetes and obesity indications in the US market.

Can I import Zepbound from the US to the UK?

Importing unlicensed prescription medicines for personal use is a complex regulatory matter in the UK. The MHRA's personal importation policy requires that a UK-licensed equivalent be unavailable and that a licensed prescriber oversees the import. Since tirzepatide for weight management is available in the UK as MHRA-licensed Mounjaro, there is no clinical justification for importing Zepbound. Importing prescription medicines without authorisation may constitute an offence.

Is Zepbound the same molecule as Mounjaro?

Yes — both Zepbound and Mounjaro contain tirzepatide, the same dual GIP/GLP-1 receptor agonist manufactured by Eli Lilly. The dosing schedule (2.5 mg starting, titrated to 15 mg weekly) is identical. The products differ only in their brand name and the specific device and packaging design for their respective markets.

What clinical trials support Zepbound?

Zepbound's FDA approval was based on the SURMOUNT programme, specifically SURMOUNT-1 (tirzepatide for obesity without diabetes) and SURMOUNT-2 (obesity with type 2 diabetes), the same dataset that underpins Mounjaro's weight-management licence in the UK. SURMOUNT-1 demonstrated mean weight reduction of approximately 20.9% at 72 weeks with 15 mg tirzepatide.

Why does the US have Zepbound while the UK has Mounjaro for weight loss?

Eli Lilly chose to use the Mounjaro brand for both the diabetes and weight-management indications in the UK and EU, whereas in the US they created a separate brand (Zepbound) for the weight-management indication to distinguish it from the diabetes brand. This is a commercial and regulatory strategy choice rather than a difference in the medicine.

Is research-grade tirzepatide the same as Zepbound?

Research-grade tirzepatide peptide for laboratory use shares the same primary amino-acid sequence as the active component in Zepbound and Mounjaro, but is not manufactured to pharmaceutical GMP standards and is not sterile or pyrogen-tested for human use. It is supplied for in-vitro and preclinical analytical research only.