Mounjaro is a once weekly injection that goes just under the skin. Take it on the same day each week, at any time of day, with or without food.

You can inject into your stomach (keeping a few centimetres clear of the navel), the front of your thigh, or the back of your upper arm if someone else is helping you. Switch the spot you use each week so the skin doesn't get sore, and avoid anywhere that's bruised, red, or hardened.

When you're ready to inject, check the solution through the window on the pen. It should be clear and colourless. If it looks cloudy or has anything floating in it, set that pen aside and don't use it. Wash your hands, attach a fresh needle, and clean the injection site with an alcohol wipe. Press the pen against your skin at a right angle, push the button, and hold it there for around ten seconds until you hear the click that tells you the dose is in. Pop the needle into a sharps bin afterwards.

If you forget a dose and remember within four days, take it as soon as you can. If more than four days have passed, skip it and carry on with your next scheduled dose. Don't double up.

For storage, keep unopened pens in the fridge between 2 and 8°C and never freeze them. Once you've started using a pen, you can either keep it in the fridge or leave it at room temperature (up to 30°C) for up to 30 days. Keep the cap on when it's not in use, and discard the pen 30 days after first use even if there are doses left.

The active ingredient in Mounjaro is tirzepatide, a synthetic version of two natural gut hormones called GLP‑1 and GIP. Your body releases these hormones whenever you eat, and they play a role in how you feel hunger, how full you feel after a meal, and how your blood sugar is regulated.

What makes Mounjaro different from other weight loss injections is that it works on both hormones at the same time. Most similar medications act on GLP‑1 alone. By activating both pathways, tirzepatide reduces appetite, slows how quickly food leaves your stomach, helps your body release insulin when blood sugar rises, and may improve how your body handles fat. It's this dual action that gives Mounjaro its edge in clinical trials.

Most people get on well with Mounjaro, especially if they follow the gradual dose schedule. Side effects are usually mild to moderate and tend to ease off within a few weeks as your body adjusts.

The most common side effects (more than 1 in 10 people) are digestive: nausea, diarrhoea, constipation, vomiting, abdominal pain, indigestion, and a reduced appetite (which is partly the point of the medication). They're most noticeable just after a dose increase and usually settle down within a week or two.

Less commonly (up to 1 in 10 people), some patients experience injection site reactions like redness or itching, tiredness, headaches, dizziness, bloating, heartburn, or low blood sugar (the last is more likely if you're already on diabetes medication).

Serious side effects are rare but worth knowing about. Pancreatitis can cause severe stomach pain that may radiate to your back, and it needs urgent medical attention. Gallbladder issues sometimes occur, particularly with rapid weight loss. Severe allergic reactions, kidney problems, and changes in vision (in patients with existing diabetes) are also possible.

A few practical tips help with the most common side effects. Eat smaller meals more often, ease off rich and fatty foods, and stay well hydrated, especially if you've had any diarrhoea. Take your injection on a day you can rest if you tend to feel rough afterwards.

If side effects feel severe or aren't improving, get in touch with your Rightangled clinician. Don't stop treatment suddenly without speaking to us first.

Mounjaro isn't suitable for everyone, and there are some situations where it shouldn't be used at all. You shouldn't take it if you or a close family member has a history of medullary thyroid carcinoma, if you have Multiple Endocrine Neoplasia syndrome type 2, or if you've previously had a serious allergic reaction to tirzepatide. It's also not safe during pregnancy, while trying for a baby, or while breastfeeding. If you're planning a pregnancy, you'll need to stop Mounjaro at least two months beforehand to allow it to clear from your system.

There are also conditions where Mounjaro can be used, but you'll need to mention them in your consultation so we can prescribe safely. These include any history of pancreatitis, severe stomach emptying problems, diabetic eye disease, kidney disease, gallstones or gallbladder problems, current use of insulin or other diabetes medications, mental health conditions including depression, or any planned surgery in the near future.

Mounjaro can affect contraception, particularly oral contraceptives, in patients with a higher BMI. If you take the pill, your clinician may recommend adding a barrier method or switching to a non oral contraceptive for a few weeks after starting Mounjaro and after each dose increase.

It's sensible to be cautious with alcohol while you're on Mounjaro. It can make low blood sugar more likely and tends to worsen any nausea you might be experiencing. Until you know how Mounjaro affects you, take care driving or operating machinery, especially during the first few weeks and after each dose increase, since some patients feel dizzy or tired.

Throughout your treatment, your Rightangled clinician will keep an eye on how you're getting on. Get in touch straight away if you notice severe stomach pain, sudden vision changes, or signs of an allergic reaction such as facial swelling or difficulty breathing.