Mounjaro (tirzepatide) is a relatively new medicine in the UK, having received regulatory approval from the Medicines and Healthcare products Regulatory Agency (MHRA) in September 2022 for type 2 diabetes and November 2023 for chronic weight management. As the first dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist approved worldwide, Mounjaro represents a significant advancement in metabolic medicine. This article explores Mounjaro's regulatory timeline, current availability through the NHS, eligibility criteria for treatment, and the clinical evidence supporting its use in UK practice.

What Is Mounjaro and When Was It Approved?

Mounjaro (tirzepatide) is a prescription medicine used for the treatment of type 2 diabetes mellitus and chronic weight management in adults. It belongs to a novel class of medications known as dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonists. This dual mechanism distinguishes Mounjaro from other diabetes and weight-loss medications currently available.

The medicine was first approved by the United States Food and Drug Administration (FDA) in May 2022 for the treatment of type 2 diabetes in adults. This marked a significant milestone as the first dual GIP/GLP-1 receptor agonist to receive regulatory approval anywhere in the world.

In the United Kingdom, Mounjaro received its marketing authorisation from the Medicines and Healthcare products Regulatory Agency (MHRA) in September 2022 for type 2 diabetes management. Subsequently, in November 2023, the MHRA expanded its licence to include chronic weight management in adults with obesity or overweight with at least one weight-related comorbidity, as an adjunct to diet and physical activity.

The medicine is administered as a once-weekly subcutaneous injection using a pre-filled pen device. It works by mimicking the action of incretin hormones, which help regulate blood glucose levels and appetite. The dual receptor activity is thought to provide enhanced metabolic benefits compared to single-receptor agonists.

Mounjaro's Development Timeline and UK Availability

The development of tirzepatide began over a decade ago, with Eli Lilly and Company conducting extensive preclinical research into dual incretin receptor agonism. The first human clinical trials commenced around 2015, with the pivotal SURPASS programme enrolling patients from 2018 onwards. This comprehensive trial series included multiple studies comparing tirzepatide against placebo, insulin, and other established diabetes medications including semaglutide.

Following FDA approval in May 2022, the European Medicines Agency (EMA) granted marketing authorisation for Mounjaro across the European Union in September 2022. The UK MHRA approval followed shortly thereafter, maintaining regulatory alignment despite Brexit. The initial indication covered adults with type 2 diabetes inadequately controlled on diet and exercise, either as monotherapy (when metformin is inappropriate) or as add-on therapy to other glucose-lowering medications.

In terms of NHS availability, Mounjaro's journey has been more gradual. The National Institute for Health and Care Excellence (NICE) published technology appraisal guidance (TA924) in October 2023, recommending tirzepatide as an option for treating type 2 diabetes in specific circumstances. For weight management, NICE issued guidance (TA1058) in March 2024, recommending Mounjaro for adults with obesity or overweight with weight-related complications, as part of a specialist weight management service.

NHS prescription availability varies by region, with some integrated care boards (ICBs) implementing the medicine more rapidly than others. Supply constraints have periodically affected availability across the UK. Patients should consult their GP or specialist diabetes team regarding local commissioning decisions and eligibility criteria for NHS-funded treatment.

Who Can Use Mounjaro in the UK?

Mounjaro is licensed for use in adults aged 18 years and over for two distinct indications, each with specific eligibility criteria.

For type 2 diabetes management, NICE guidance (TA924) recommends tirzepatide as a treatment option when:

• It is prescribed according to the GLP-1 receptor agonist criteria in NICE guideline NG28

• Patients have inadequate glycaemic control despite optimised therapy

• Treatment may be initiated in primary or secondary care, depending on local pathways

For chronic weight management, NICE guidance (TA1058) recommends Mounjaro for adults with:

• BMI of 35 kg/m² or greater, or

• BMI of 30–34.9 kg/m² with at least one weight-related comorbidity (such as hypertension, dyslipidaemia, obstructive sleep apnoea, or cardiovascular disease)

• For people from South Asian, Chinese, other Asian, Middle Eastern, Black African, or African-Caribbean family backgrounds, the BMI thresholds are reduced by 2.5 kg/m²

• Access must be through a specialist weight management service that provides multidisciplinary support

Treatment should only continue if patients achieve the weight loss specified in the NICE guidance after the initial treatment period.

UK contraindications include:

• Hypersensitivity to tirzepatide or any excipients

• Pregnancy (women of childbearing potential should use effective contraception)

Important precautions and warnings:

• Tirzepatide may reduce the absorption of oral contraceptives; women should use additional contraceptive methods for 4 weeks after starting treatment and after each dose increase

• Breastfeeding is not recommended during treatment

• Caution in patients with thyroid disease (monitoring advised)

• Patients with severe renal impairment or gastroparesis require careful assessment before initiation

• Those with a history of pancreatitis should be monitored closely

• Age over 75 years requires cautious dose titration due to limited clinical trial data

For weight management, prescribing must be initiated within specialist weight management services. For diabetes, initiation may occur in primary care where local pathways allow.

Safety Profile and Clinical Evidence

The safety profile of Mounjaro is based on extensive clinical trial data involving over 10,000 participants across the SURPASS and SURMOUNT programmes. The most commonly reported adverse effects are gastrointestinal in nature, occurring particularly during dose escalation. According to the UK SmPC, these include:

• Nausea (very common: may affect more than 1 in 10 people)

• Diarrhoea (very common)

• Vomiting (common: may affect up to 1 in 10 people)

• Constipation (common)

• Abdominal pain (common)

These effects are typically mild to moderate in severity and tend to diminish over time as the body adjusts to treatment. Starting at a low dose (2.5 mg weekly) and gradually increasing every 4 weeks helps minimise gastrointestinal symptoms.

Hypoglycaemia risk is generally low when Mounjaro is used alone or with metformin, but increases when combined with insulin or sulfonylureas. Dose reduction of these concomitant medications may be necessary. Patients should be educated about recognising and managing hypoglycaemic episodes.

More serious but rare adverse effects include:

• Acute pancreatitis (discontinue immediately if suspected)

• Gallbladder disease (cholecystitis, cholelithiasis)

• Acute kidney injury (usually secondary to dehydration from gastrointestinal effects)

• Diabetic retinopathy complications (in patients with pre-existing retinopathy experiencing rapid glucose improvement)

Clinical efficacy has been robust across trials. In the SURPASS-2 study, tirzepatide achieved HbA1c reductions of 2.0–2.5% (22–27 mmol/mol) from baseline, superior to semaglutide 1 mg. Weight loss ranged from 7.6 to 12.9 kg depending on dose (5–15 mg weekly). The SURMOUNT-1 trial demonstrated average weight reductions of 15–22.5% over 72 weeks in adults with obesity.

Patient safety advice includes:

• Report persistent severe abdominal pain immediately (possible pancreatitis)

• Maintain adequate hydration, especially during gastrointestinal symptoms

• Monitor for signs of hypoglycaemia if taking insulin or sulfonylureas

• Contact your GP if experiencing persistent vomiting preventing oral intake

• Attend regular monitoring appointments for weight, HbA1c, renal function, and treatment response assessment

• Report any suspected side effects via the MHRA Yellow Card Scheme

Cardiovascular outcome data from the SURPASS-CVOT trial are being collected to provide further evidence regarding Mounjaro's safety profile in high-risk populations.

Frequently Asked Questions