Mounjaro

Mounjaro contains tirzepatide, a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for chronic weight management in adults with a body mass index (BMI) of 30 kg/m² or above, or 27 kg/m² or above in the presence of at least one weight-related comorbidity such as type 2 diabetes, hypertension, or dyslipidaemia.

How Mounjaro Works

By activating both GIP and GLP-1 receptors simultaneously, tirzepatide reduces appetite, slows gastric emptying, and enhances glucose-dependent insulin secretion. This dual mechanism produces greater weight loss than single-receptor GLP-1 agonists. In clinical trials, patients lost an average of 20–22% of their body weight over 72 weeks, making Mounjaro one of the most effective pharmacological weight management tools currently available.

Who It Is For

Mounjaro is prescribed alongside a reduced-calorie diet and increased physical activity. It is not a standalone solution but forms part of a comprehensive weight management programme. It is also approved in the UK for the treatment of type 2 diabetes to improve blood glucose control.

How to Use Mounjaro

Mounjaro (tirzepatide) is given as a subcutaneous (under-the-skin) injection once weekly, on the same day each week. Injections can be given at any time of day, with or without food. Suitable injection sites are the abdomen, thigh, or upper outer arm — rotate the site each week to reduce local reactions.

Dose Escalation

Treatment begins at 2.5 mg once weekly for four weeks. The dose is then increased in steps to allow the body to adjust and minimise side effects. The typical titration schedule is 2.5 mg for 4 weeks, then 5 mg for 4 weeks, increasing by 2.5 mg increments every four weeks as tolerated, up to the prescribed maintenance dose (commonly 10 mg or 15 mg weekly).

Do not skip the gradual titration — starting at a higher dose without building up significantly increases the risk of nausea and vomiting. Store pens in the fridge and allow to reach room temperature before injecting.

Mounjaro KwikPen is available in six dose strengths: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg per 0.5 mL. Each pre-filled pen delivers a single weekly dose. The pens are for single use and must be disposed of safely after each injection. Store in the refrigerator (2°C–8°C) and do not freeze. Pens may be kept at room temperature (up to 30°C) for up to 21 days if needed.

Common Side Effects

The most frequently reported side effects are gastrointestinal, generally mild to moderate in intensity, and most common during the dose escalation phase:

• Nausea (very common, especially when doses are increased)
• Vomiting
• Diarrhoea
• Constipation
• Abdominal pain or discomfort

Taking smaller meals, avoiding high-fat foods, and eating slowly all help reduce nausea.

Serious Risks

Pancreatitis has been reported — seek immediate medical attention if you develop severe persistent abdominal pain that radiates to the back. Mounjaro is associated with a small increased risk of gallstones. Do not use Mounjaro if you or a family member has a history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Hypoglycaemia (low blood sugar) is more likely if you are also taking insulin or a sulphonylurea — discuss dose adjustments with your doctor.

Mounjaro is contraindicated in patients with a personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2). It should not be used during pregnancy or breastfeeding. Use with caution in patients with a history of pancreatitis. Tirzepatide slows gastric emptying and may affect the absorption of oral medications; consult your doctor about timing of other drugs. Not currently licensed for use in patients under 18 years of age.

Do not use Mounjaro if you have a personal or family history of medullary thyroid carcinoma or MEN 2 syndrome. It is contraindicated in patients with known hypersensitivity to tirzepatide or any excipient. Not indicated during pregnancy or breastfeeding. Use with caution in patients with severe gastrointestinal disease or active gallbladder disease.