Mounjaro (tirzepatide) is a weight loss treatment that comes in the form of a weekly self-injectable pen.

We can prescribe Mounjaro if it’s suitable for you. Find out more about our weight loss treatment service. Find out more about our weight loss treatment service.

Mounjaro is an injection pen used for weight loss and to treat type 2 diabetes.

They are exactly the same medicine containing the same active ingredient (tirzepatide) and work in exactly the same way. The difference is the name: Zepbound is the US name for the weight loss management medicine, whereas in the UK it’s licensed under the name Mounjaro. Zepbound is not licensed in the UK.

The active ingredient in Mounjaro is called tirzepatide.

Tirzepatide works on two different hormonal receptors: glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). You may have heard of GLP-1 from other weight loss injections.

GLP-1 helps to regulate blood sugar levels, which in turn talks to the brain to make you feel less hungry and prevent cravings. It also slows down the emptying of the stomach to keep you feeling fuller for longer.

GIP regulates energy balance in brain and fat cells, enhancing the GLP-1 effect of suppressing your appetite and improving sugar control.

By mimicking the effects of both these naturally occurring hormones, Mounjaro has been shown to have greater weight loss potential than medicines that work on GLP-1 alone.

You inject Mounjaro under the skin (subcutaneously) in your stomach area, thigh or upper arm once a week using an injection pen. Don’t worry, it’s actually much easier than it sounds and if we prescribe Mounjaro for you, we’ll provide you with full instructions on how to use it.

You must follow a strict dosage increase schedule as advised by your healthcare provider.

To allow your body to get used to the medicine and have the best chance for long-term success, you should follow the gently increasing dosage schedule as instructed.

Usually, you’ll start with a dose of 2.5 mg of Mounjaro, which will increase every four weeks (or as advised and if suitable for you) until you reach your maximum maintenance dose of 5mg, 10mg or 15mg.

If you’re wondering how much weight you can lose on Mounjaro, clinical trials have shown that patients could achieve at least 20% weight loss after using tirzepatide for 72 weeks (18 months) when combined with healthy lifestyle changes.

Mounjaro can cause some side effects to occur. Very common ones are gastrointestinal in nature: nausea, vomiting, diarrhoea and constipation. These are mainly seen with dose increases, and tend to settle with time.

Other common side effects could include: fatigue, feeling lightheaded, excess wind (flatulence), gallstones, gastroesophageal reflux, injection site reactions, hair loss and hypoglycemia in patients with type 2 diabetes.

In rare cases, there can be serious side effects, such as:

Pancreatitis – if you develop severe abdominal pain, with or without persistent vomiting, this may be a sign of pancreatitis and you need to get medical help immediately.

Anaphylaxis – if you experience difficulty breathing, swelling of the face, lips or tongue and difficulty swallowing, you may be having a severe allergic reaction (anaphylaxis) and you must seek immediate medical help.

Please read the Patient Information Leaflet that comes with your medicine for full details of side effects and how to use Mounjaro.

Mounjaro is approved for people with a BMI over 30 (obesity), as well as those with a BMI over 27 (overweight) who also have weight-related health problems such as prediabetes, high blood pressure, high cholesterol, or heart problems.

You shouldn’t use tirzepatide if you’re pregnant, and you should stop taking Mounjaro at least one month before trying to get pregnant.

Mounjaro is not suitable in some medical circumstances, for example if you use some other diabetes medicines, have severe problems with digesting food, or have a history of pancreatitis or thyroid cancer. If you’re allergic to tirzepatide or any of the other ingredients in this weight loss injection treatment, you must not use Mounjaro.

It’s essential that you give us a full medical history and details of any conditions or other medicines you’re taking when you fill out our online questionnaire. This ensures we’re able to prescribe weight loss treatment that’s suitable and safe for you.

As Mounjaro is a new weight loss medicine available in the UK, it has been assigned a black triangle, which means it will be closely monitored for any adverse effects.

We can also prescribe other medicines to help support your weight loss and weight management journey. Wegovy and Saxenda are weight loss injection treatments that work similarly to Mounjaro. Orlistat and Xenical are capsule medicines that work by helping your body get rid of the extra fat in your diet.

Find out more about weight loss treatments we offer.

We’ve also teamed up with WeightWatchers to help support your weight loss journey. If we prescribe any weight loss treatment for you, you can enjoy an exclusive discount at WeightWatchers from only £7/month for your first 6-months. *Please see Terms and Conditions

Making healthy lifestyle changes, such as improving your diet and increasing activity, can help with weight loss and also help you to live a healthier, happier life.

At Boots Online Doctor, we offer more than medicine. Check out our free online webinars where our expert Lifestyle Medicine team offers advice and guidance on weight loss. We also have a free 10-week weight loss programme filled with helpful videos and articles. You may also want to read about how diet affects your mood and our recommended eating guides.

Common Mounjaro side effects should be mild and are likely to lessen or even disappear after your body gets used to the treatment. We understand that it’s still tough to live with these discomforts though and so we’ve put together some tips for managing these where possible:

• Make sure to inject yourself with the treatment at the same time and day each week so your body has a regular interval between each dose
• Stay hydrated, sipping water and other clear liquids if you’re experiencing nausea, vomiting or diarrhoea. It may also help to eat smaller meals more regularly and avoid anything that smells or tastes too strong
• If you’re struggling with constipation, increase your fibre intake, stay well hydrated and try eating small fruits such as prunes, figs or grapes. Make sure you’re also getting regular activity, such as going on short walks
• To ease a headache, spend time in a quiet space to relax, take a simple pain relief medicine like paracetamol, drink plenty of water, and try relaxation techniques such as meditation and DIY scalp massage

For more information on managing side effects and what to do if you experience more severe side effects, see our dedicated weight loss medicine side effects page.

The best places to inject Mounjaro are ones with the most fat. These are: your tummy (although make sure to inject more than 5cm away from your belly button); the front of your thighs; or your upper arms. It’s important that you change injection sites regularly. You can inject in the same area (e.g. tummy) but choose a different spot in that area each time.

Mounjaro should start working straight away, but it could take several weeks until it has a noticeable effect on regulating your blood sugar level and impacting your appetite and eating habits.

If you’re using Saxenda or Wegovy and don’t have any significant side effects, you can switch to Mounjaro on your next weekly scheduled injection day. If you have side effects you should wait for these to pass before switching to Mounjaro.

All patients using Mounjaro for the first time will start with 2.5mg. Keep in mind, Mounjaro may not be suitable for you (even if you're using another weight loss medicine). We’ll assess if it’s right for you during your consultation.

Wegovy and Mounjaro are both weekly injection pens and work in similar ways to aid weight loss. Mounjaro has proven more effective in clinical trials, as it works on GLP-1 and GIP hormones, whereas Wegovy only works on GLP-1. However, Mounjaro is a new medicine in the UK so we don’t have as much safety data on it compared to other medicines in the long term. Deciding if or which medicine is right for you will depend on different factors, which we’ll assess during your consultation. If you’re already on Wegovy (or Saxenda) and losing weight, we recommend you keep using it. Keep in mind, weight plateaus are normal on your weight loss journey.

The ‘instructions for use’ that come with the pen advise that you use swabs - you can purchase these in your Boots store when you collect your pen, or online.