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Mounjaro (Tirzepatide)

What is Mounjaro aka Tirzepatide?


The well-publicised Semaglutide may be about to get some strong competition. Mounjaro is a weekly self–injectable pen used for weight loss. It contains tirzepatide which works by regulating blood sugar and energy balance levels, helping to reduce appetite and prevent cravings.​

How does Mounjaro work?

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.

During clinical trials to evaluate the effectiveness of Tirzepatide when used for treating obesity, participants without diabetes lost on average 52lbs after 16 months - or 22.5 per cent of their weight - compared to those who took the placebo. The highest-dose of the weekly injection, known as tirzepatide (brand name Mounjaro), saw obese adults drop more than a fifth of their bodyweight in little over a year.

The latest study involved 2,539 adults, although none had diabetes

Volunteers given the highest dosage of tirzepatide lost 52lbs after 16 months - or 22.5 per cent of their weight - while those given weaker shots dropped between 35 and 49lbs.

Commenting on the latest study, Professor Sir Stephen O’Rahilly, Director of the Medical Research Council Metabolic Diseases Unit at Cambridge University, said: “The results of this trial are very impressive. Treatment of people with obesity with a weekly injection of tirzepatide produced weight loss similar to that seen with weight loss surgery. Blood tests showed improvements in all the markers of metabolic and cardiovascular health. This study, and recent similar reports of a related agent semaglutide, provide secure evidence that people with obesity can be effectively and safely treated using a medication that is based on the modification of naturally occurring hormones."


How do I use Mounjaro?

Just like Ozempic, Wegovy, Saxenda and Trulicity, 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.

What dose of Mounjaro would I need?

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.

Would I be suitable to use Mounjaro?

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.

Does Mounjaro have any side effects?


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.

How would I manage any side effects?


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 aftercare page for our customers.

How long until I start seeing results?


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.

Can I switch from other weight loss medications to Mounjaro?


If you’re using Saxenda or Wegovy, you’ll need to wait 1 month before switching to Mounjaro. This is called the 'washout' period, and gives the body time for the first drug to leave the system. 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.

Which medication is the best one for weight loss?


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.

What do the results show for Mounjaro?

Tirzepatide has been mentioned in a lot of media articles since 2022. You can find a selection of them below:

Tirzepatide Powers 'Unprecedented' Weight Loss in Obesity Trial (

Tirzepatide new treatment option for people who are overweight or have obesity: SURMOUNT-1 clinical trial (

Focus On - tirzepatide, semaglutide (

Diabetes drug leads to notable weight loss in people with obesity – study | Medical research | The Guardian

Diabetes drug could be a game changer for obesity, new study shows (

Tirzepatide Once Weekly for the Treatment of Obesity | NEJM

Game-changing drug can help Brits shed up to 52lbs, experts say (

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