Mounjaro

Mounjaro is the brand name for tirzepatide, a prescription-only medicine given as a once-weekly injection under the skin. In the UK it is licensed for weight management in adults alongside a reduced-calorie diet and increased physical activity, and separately for type 2 diabetes. It is supplied in a pre-filled pen and is not available without a prescription.

Tirzepatide mimics two gut hormones your body already produces after eating - GIP and GLP-1. Acting on both receptors slows how quickly the stomach empties and dampens appetite signalling in the brain, so you tend to feel full sooner and stay full for longer. Most people find they simply want less food, rather than having to resist it. It is a tool that makes eating less achievable; it does not do the work on its own.

One injection a week, on the same day each week, at any time of day and with or without food. It goes into the fatty tissue of the abdomen, thigh or upper arm, and you should rotate the site each week. If you miss a dose you can usually take it within four days; after that, skip it and go back to your normal day. Never take two doses close together to catch up. Pens are kept in the fridge, and your full instructions come with your order.

In the manufacturer's large weight-management trials, adults taking the higher doses lost roughly a fifth of their body weight on average over about 18 months, alongside diet and activity changes. That is an average across thousands of people - some lost considerably more, some noticeably less, and a minority did not respond. Weight tends to come off gradually rather than in a rush, and the first few weeks on a starting dose are often about tolerance rather than results. Anyone promising you a specific number is guessing.

The common ones are digestive: nausea, diarrhoea, constipation, indigestion, burping and a reduced appetite. They are usually mild to moderate, most likely in the days after a dose increase, and often settle as your body adjusts. Eating smaller portions, avoiding rich or fatty food and keeping fluids up all help. Less commonly, gallbladder problems and pancreatitis can occur - severe, persistent abdominal pain that radiates to your back needs urgent medical attention. Tell your prescriber about any medicines you already take, as timing can matter.

Treatment is generally considered for adults with a BMI of 30 or above, or 27 and above where there is a weight-related health condition such as high blood pressure, sleep apnoea or type 2 diabetes. It is not suitable during pregnancy, when breastfeeding or when trying to conceive, and there are conditions and medicines that rule it out or need extra care. Eligibility is decided by a prescriber from your consultation answers, not by the calculator on this page - that is a guide only.

Weight management with tirzepatide is treatment for a long-term condition, not a short course. Appetite tends to return when it stops, and studies show most people regain a meaningful share of the weight they lost after stopping. Some people stay on it long term, some step down to a lower maintenance dose, and some come off it with a plan to hold their weight through diet and activity. That decision is one to make with your prescriber rather than on your own.