Mounjaro (tirzepatide) is a prescription medicine licensed in the UK for treating type 2 diabetes and chronic weight management in adults with obesity or overweight with weight-related comorbidities. As a dual GIP and GLP-1 receptor agonist, Mounjaro helps regulate blood glucose levels, reduce appetite, and promote significant weight loss through once-weekly subcutaneous injections. This innovative medication offers a comprehensive approach to metabolic health, addressing both glycaemic control and weight reduction. Understanding what Mounjaro helps with, who can benefit, and how it works is essential for patients and healthcare professionals considering this treatment option.

What Is Mounjaro and How Does It Work?

Mounjaro (tirzepatide) is a prescription medicine licensed in the UK for the treatment of type 2 diabetes and, more recently, for chronic weight management in adults with obesity or overweight with weight-related comorbidities. It is administered as a once-weekly subcutaneous injection and represents a novel class of medication known as a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist.

The mechanism of action of Mounjaro involves mimicking two naturally occurring incretin hormones that play crucial roles in glucose regulation and appetite control. GLP-1 stimulates insulin secretion when blood glucose levels are elevated, suppresses glucagon release (which reduces glucose production by the liver), slows gastric emptying (particularly pronounced after initial doses), and promotes satiety. GIP also enhances insulin secretion and may influence fat metabolism and energy balance. By activating both pathways simultaneously, tirzepatide offers a dual approach to metabolic regulation that distinguishes it from single-receptor GLP-1 agonists.

The combined action on these receptors results in improved glycaemic control, reduced appetite, and significant weight reduction. Clinical studies have demonstrated that this dual agonism produces greater efficacy in both glucose lowering and weight loss compared to GLP-1 receptor agonists alone. Mounjaro is available in several dose strengths, allowing for gradual titration to minimise gastrointestinal side effects while optimising therapeutic benefit. It is important to note that Mounjaro is not insulin and should not be used to treat type 1 diabetes or diabetic ketoacidosis.

What Conditions Does Mounjaro Help With?

Mounjaro is primarily indicated for two distinct but related conditions in the UK, as authorised by the Medicines and Healthcare products Regulatory Agency (MHRA).

Type 2 Diabetes Mellitus: Mounjaro is licensed as an adjunct to diet and exercise to improve glycaemic control in adults with type 2 diabetes. It can be used as monotherapy when metformin is not tolerated or contraindicated, or in combination with other glucose-lowering medications including metformin, SGLT2 inhibitors, or basal insulin. The medication helps reduce HbA1c levels (a measure of long-term blood glucose control) and may reduce the need for additional diabetes medications over time.

Chronic Weight Management: Mounjaro is also approved for weight management in adults with a body mass index (BMI) of 30 kg/m² or greater (obesity), or a BMI of 27 kg/m² or greater (overweight) in the presence of at least one weight-related comorbidity such as hypertension, dyslipidaemia, obstructive sleep apnoea, or cardiovascular disease. It should be used alongside a reduced-calorie diet and increased physical activity.

While Mounjaro has shown promising results in clinical trials regarding various metabolic parameters, it is not currently licensed specifically for cardiovascular risk reduction in the UK. Patients should not use Mounjaro for cosmetic weight loss or without appropriate medical supervision. There is no official indication for Mounjaro in conditions outside its licensed uses, and off-label use should only occur under specialist guidance.

How Effective Is Mounjaro for Type 2 Diabetes and Weight Loss?

Clinical trial evidence demonstrates that Mounjaro is highly effective for both glycaemic control and weight reduction, often exceeding the efficacy of existing treatments.

Efficacy in Type 2 Diabetes: In the SURPASS clinical trial programme, Mounjaro achieved substantial reductions in HbA1c across all dose levels. Patients treated with the highest dose (15 mg weekly) experienced average HbA1c reductions of approximately 20-25 mmol/mol from baseline, with a significant proportion achieving HbA1c targets below 53 mmol/mol (7.0%). These results were superior to comparator medications including semaglutide (a GLP-1 receptor agonist) and insulin glargine. Importantly, Mounjaro's glucose-dependent mechanism means it carries a low risk of hypoglycaemia when used without insulin or sulphonylureas.

Efficacy in Weight Loss: Weight reduction with Mounjaro is substantial and dose-dependent. In the SURMOUNT trials evaluating tirzepatide for weight management, participants without diabetes lost an average of 15–22% of their initial body weight over 72 weeks, depending on the dose used. Even at lower doses, weight loss typically exceeded 10% of baseline weight. For individuals with type 2 diabetes, weight loss ranged from approximately 5–15%, which is clinically meaningful and associated with improvements in cardiovascular risk factors.

These outcomes represent some of the most impressive results seen with pharmacological interventions for metabolic disease. However, individual responses vary, and not all patients will achieve these average results. For type 2 diabetes, NICE guidance recommends continuing treatment only if there is an HbA1c reduction of at least 11 mmol/mol (1.0%) and weight loss of at least 3% after 6 months of treatment.

Who Can Use Mounjaro in the UK?

Mounjaro is available in the UK through NHS prescription and private healthcare pathways, but eligibility criteria apply based on clinical need and NICE recommendations.

For Type 2 Diabetes: Adults with type 2 diabetes may be considered for Mounjaro when:

• Metformin and other first-line treatments have not achieved adequate glycaemic control

• There is a clinical need for significant weight loss alongside glucose management

• The patient has a BMI ≥35 kg/m² (or ≥32.5 kg/m² in people of South Asian or other high-risk ethnic backgrounds) and weight loss would benefit other obesity-related comorbidities

• The patient has a BMI <35 kg/m² and insulin would have significant occupational implications, or weight loss would benefit other obesity-related comorbidities

NICE guidance (TA924) recommends tirzepatide as an option for managing type 2 diabetes in specific circumstances, particularly when weight management is a priority.

For Weight Management: Mounjaro may be prescribed for chronic weight management in adults who meet BMI criteria (≥30 kg/m² or ≥27 kg/m² with comorbidities) and have not achieved adequate weight loss through diet and exercise alone. Access via the NHS may be limited initially, with specialist weight management services prioritising those with the greatest clinical need.

Contraindications and Cautions: Mounjaro should not be used in individuals with:

• Hypersensitivity to tirzepatide or any of the excipients

• Type 1 diabetes or diabetic ketoacidosis

• Pregnancy or breastfeeding

Caution is advised in patients with a history of pancreatitis, severe renal impairment, diabetic retinopathy, or severe gastrointestinal disease including gastroparesis. Women of childbearing potential should use effective contraception, noting that tirzepatide may reduce the effectiveness of oral contraceptives. An additional barrier method is recommended for 4 weeks after starting treatment and after each dose increase. A thorough medical assessment by a GP or specialist is essential before starting Mounjaro.

What Are the Common Side Effects of Mounjaro?

Like all medications, Mounjaro can cause side effects, although not everyone experiences them. The most frequently reported adverse effects are gastrointestinal in nature and tend to be most pronounced during dose escalation.

Very Common Side Effects (affecting more than 1 in 10 people):

• Nausea — often mild to moderate and typically improves over time

• Diarrhoea — may be transient; maintaining hydration is important

• Vomiting — usually resolves as the body adjusts to treatment

• Decreased appetite — this is part of the therapeutic effect but can be uncomfortable

• Constipation — adequate fluid and fibre intake can help

• Abdominal pain or discomfort

• Dyspepsia (indigestion)

These gastrointestinal symptoms are generally dose-dependent and can be minimised by following the recommended titration schedule, eating smaller meals, and avoiding high-fat foods.

Less Common but Important Side Effects:

• Hypoglycaemia — risk increases when Mounjaro is used with insulin or sulphonylureas; dose adjustments of these medications may be necessary

• Injection site reactions — redness, itching, or swelling at the injection site

• Fatigue or dizziness

• Increased heart rate — usually mild

Serious Side Effects (rare but requiring immediate medical attention):

• Pancreatitis — severe, persistent abdominal pain radiating to the back, often with nausea and vomiting. Stop Mounjaro and contact your GP or call 111 immediately if this occurs.

• Gallbladder problems — symptoms include upper abdominal pain, fever, and jaundice

• Severe allergic reactions — difficulty breathing, swelling of the face or throat, rapid heartbeat. Call 999 immediately if you experience these symptoms.

• Diabetic retinopathy complications — worsening of vision in people with pre-existing diabetic eye disease

• Acute kidney injury — particularly in the context of severe dehydration from vomiting or diarrhoea

Patient Safety Advice: If you experience persistent vomiting or diarrhoea, ensure adequate fluid intake and contact your healthcare provider. Report any suspected side effects to the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk. Regular monitoring of blood glucose, renal function, and weight is recommended during treatment. Always inform your GP or diabetes specialist of any new symptoms or concerns.

Frequently Asked Questions