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Mounjaro injections are one of the most requested weight loss treatments we offer, so here’s what to expect.
Considering Mounjaro injections? Here’s what they are, how they work, and what to expect from treatment.
Mounjaro is a prescription-only injectable medication used for weight management, and one of the most widely discussed treatments in this category. This guide covers what it is, how the injection works, and what to expect if you’re considering it.
Mounjaro is the brand name for tirzepatide, a medicine that acts on two separate gut-hormone receptors — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — rather than just one. Both hormones are released naturally after eating and play a role in appetite regulation, insulin release, and slowing stomach emptying. Mounjaro was originally developed and licensed for managing type 2 diabetes, and its effect on weight became a well-documented secondary benefit that led to its use in weight management.
Mounjaro is delivered using a pre-filled, single-use pen, injected once a week under the skin (subcutaneously) — typically into the abdomen, thigh, or upper arm. It doesn’t need to be taken with food or at a specific time of day, but should be injected on the same day each week for consistency. For a full breakdown of the dose titration schedule, see our complete Mounjaro dosing guide.
Mounjaro is generally considered for adults with a BMI of 30 or above, or a BMI of 27 or above alongside a weight-related health condition such as high blood pressure or type 2 diabetes. Suitability is always confirmed through a clinical assessment rather than a self-check — see our full eligibility criteria for more detail.
In published clinical trial data (the SURMOUNT programme), participants without diabetes lost an average of up to around 21% of their starting body weight at the highest dose over 72 weeks, when combined with diet and exercise. Individual results vary considerably, and these figures describe trial averages rather than a guaranteed personal outcome.
The most frequently reported side effects are gastrointestinal — nausea, diarrhoea, constipation, and reduced appetite — particularly during the early weeks of treatment or after a dose increase. These are usually described as mild to moderate and tend to ease as the body adjusts. Less common but more serious risks can include gallbladder problems and pancreatitis, which is why ongoing clinical review is part of every prescription.
Mounjaro (tirzepatide) acts on two hormone pathways, while Wegovy (semaglutide) acts on one. See our full Mounjaro vs Wegovy comparison for more detail.
Most people begin to notice initial effects within the first few weeks, though meaningful weight loss typically builds gradually over several months as the dose is titrated up.
Mounjaro is intended to be used alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment. Your prescriber can advise on lifestyle support alongside your treatment plan.
Want to know if Mounjaro is right for you? Start your free eligibility assessment.
Before starting Mounjaro injections, you’ll complete a short online eligibility assessment covering your BMI, medical history, and current medications, which a prescriber reviews individually. Once approved, your Mounjaro injections are dispensed with clear instructions on injection technique, storage, and what to do if you miss a dose. Most people self-administer Mounjaro injections at home, using the pre-filled pen in the thigh, abdomen, or upper arm, rotating the injection site each week. If you’re new to self-injecting, your care team can talk you through the process before your first dose. As with other GLP-1 treatments, Mounjaro injections are best combined with a reduced-calorie diet and regular physical activity, rather than relied on alone.