Mounjaro contains the medicine tirzepatide. It’s a once-weekly injection used to support weight loss in eligible patients, and it works in a similar way to Wegovy by reducing appetite and helping people feel fuller for longer.

Tirzepatide activates two receptors in the body:

- GLP-1 (glucagon-like peptide-1)

- GIP (glucose-dependent insulinotropic polypeptide)

These receptors are involved in regulating blood sugar levels and curbing appetite, which can help reduce hunger and cravings over time.

Mounjaro at a glance

~20–25% weight loss after the first year (varies by individual and depends on dose, adherence and lifestyle changes)

Once-weekly injection

Maintenance doses: 5mg, 10mg, 15mg weekly (your prescriber will recommend what’s right for you)

Typical age limit: 18+ (subject to clinical assessment and eligibility)

Yes, like all medications, Mounjaro can cause side effects, though not everyone experiences them. Common effects include nausea, constipation, diarrhoea, headache, fatigue, vomiting, and abdominal discomfort. Side effects are often more noticeable during titration and commonly improve over time.

• Headaches
• Vomiting
• Diarrhoea
• Constipation
• Nausea
• Abdominal pain
• Fatigue
• Weakness


These side effects usually reduce in frequency over time and are mainly seen during the dose titration period. Although most patients tolerate the medication very well, if you do have any side effects then don’t worry, you can speak to the Slimmr prescribing team who can help you and offer advice on how to manage them.

Many people feel nervous at first, but it’s usually straightforward and the needles are very small. Patients receive a step-by-step guide with their medication. If they need support, the prescribing team can talk them through it and, where appropriate, arrange additional help. There's lots more detail in our medication guides.

Common sites include:

- Upper arms
- Tummy/abdomen (3-5cm away from your belly button)
- Upper legs (front of thighs)

Patients may prefer one site over another; rotating sites can help reduce irritation. We tend to find the tummy region is easiest. Pinch the area between your thumb and fingers then with the other hand, inject at a 90 degree angle into the area you’re holding. It is recommended that you use a slightly different injection site each week – we call this ‘rotating’ the injection site. You do this by moving the point where you inject by at least 3cm every time and this helps avoid injecting into the same area repeatedly. For example, if injecting into your upper arm, the first injection site may be regarded as 12 o’clock. Next time, shift the injection site down and to the right, as if it is 3 o’clock, and the subsequent injection would be at 6 o’clock, and so on. If you’re injecting into your tummy, do one side one week and switch to the other side the next.