PLEASE NOTE – The information contained within this webpage is intended for medical professionals only. Non-medical professionals should not read further. 

Additionally, the information contained within this page is intended for educational purposes and as a quick reference for medical professionals. All information contained within should be double-checked against advice boards such as MHRA, NICE, and the NHS. All indications and access may change.  
Finally, nothing on this page has been written with the intent of advertisement. Mounjaro® is a Prescription Only Medicine (POM) product and its misuse can be very dangerous. 

Mounjaro® is one of the newest generations of medicines which has been approved for use in encouraging patient weight loss. A dual-agonist, this medicine is given as a weekly injection alongside a reduced-calorie diet food plan and increased physical exercise. Studies have demonstrated Mounjaro®’s ability to suppress appetite by decreasing gastric emptying, and its ability to help manage blood sugar levels, among other benefits. In this article, we will be briefly summarising some of the main talking points of Mounjaro®, answering frequently asked questions, and discussing some of the studies and literature that have underpinned the discussion around Mounjaro®. 

How does Mounjaro® work? Mechanism of Action 

Mounjaro® is the market name for Tirzepatide, a medicine commonly used in treating Type 2 diabetes. Mounjaro® is a dual agonist which effects two receptors within the body, these being GIP (glucose-dependent insulinotropic polypeptide) receptor and GLP-1 (glucagon-like peptide-1) receptors. This leads to an increased sensitivity and production of insulin, resulting in lower blood sugars, and slower gastric emptying, which in turn leads to a sensation of fullness and satiety for longer. When used alongside increased physical activity and a reduced-calorie diet, this medicine can be effective to help people lose weight more effectively. 

Mounjaro® is administered once per week, in doses ranging between 2.5mg and 15mg. Mounjaro® is often self-injected and needs to be administered personally by the patient. Administration utilises a pre-dosed injection pen, and it is typically injected in the upper thigh, stomach, or upper arm. Patients are often given lower doses of Mounjaro® for the first month of their course, and after that adjustment period, the dose may be increased until their maximum maintenance dose is found for weight loss. 

The Clinical Evidence & Effectiveness for Mounjaro® in Weight Loss Contexts 

A doctor in a white labcoat measures the waist of a woman using blue tape. They both stand in a bright room.

Mounjaro® was approved for use in weight loss in the UK on the Eighth of November 2023; this approval by the MHRA followed several international studies into the efficacy of this weight loss drug. 

  • In 2022 study on Tirzepatide a randomised control trial of 2539 adults was undertaken. In this double-blind study, the group was divided into two, a placebo group and a Tirzepatide group. The Tirzepatide group lost −15.0% of their mean body weight after 72 weeks. High proportions of the Tirzepatide group achieved a ≥5% loss; while the placebo group comparatively lost −3.1% under the same conditions.(Tirzepatide Once Weekly for the Treatment of Obesity | New England Journal of Medicine) 

Overall, the body of evidence favours Mounjaro’s efficacy as a weight loss drug. However, there are studies which indicate coming off of this drug may cause patients to put weight back on.  

More on this: Mounjaro® health benefits found to reverse one year after stopping drug - The Pharmaceutical Journal 

Mounjaro® - Safety, Side Effects & Monitoring 

Mounjaro® has many side effects, some of which are similar to Wegovy (such as an impact on gastrointestinal function). We will be listing some of the side effects for Mounjaro® below.  

Please note, the side effects below have been informed by product information leaflets from Mounjaro® products.  

As these may be out of date, please always check supplier-provided product information leaflets, as well as other reputable sources for an extensive list of potential side effects. 

Serious side effects  
Uncommon (~1 in 100) 

  • Acute pancreatitis - this is a condition which could cause severe pain in the stomach and back which does not go away. You should see a doctor immediately if you experience such symptoms.  

Stop using this medicine and seek urgent medical help if you experience severe, persistent pain in the stomach area (abdomen), with or without nausea and vomiting. This could be a sign of acute pancreatitis, which is serious and potentially life-threatening.  

Rare (may affect up to 1 in 1000 people) 

  • Severe allergic reactions (e.g. anaphylactic reaction, angioedema) - you should get immediate medical help and inform your doctor if you experience symptoms such as breathing problems, rapid swelling of the lips, tongue and/or throat with difficulty swallowing and a fast heartbeat.  

Other Side Effects  
Very common (may affect more than 1 in 10 people) 

  • Low blood sugar (hypoglycaemia) when Tirzepatide is used for the treatment of type 2 diabetes with medicines that contain a sulphonylurea and/or insulin. If you are using a sulphonylurea or insulin, the dose may need to be lowered while you use Tirzepatide.  
    Symptoms of low blood sugar may include headache, drowsiness, weakness, dizziness, feeling hungry, confusion, irritability, fast heartbeat and sweating. Your doctor should tell you how to treat low blood sugar. 
  • Feeling sick (nausea)*  
  • Diarrhoea*  
  • Being sick (vomiting) – this usually goes away over time*  
  • Stomach (abdominal) pain* 
  • Constipation*  

*These side effects are usually not severe. They are most common when first starting Tirzepatide but decrease over time in most patients. 

  • Constipation, abdominal pain, and vomiting are very common in patients treated for weight management, but common in patients treated for type 2 diabetes.  

Common (may affect up to 1 in 10 people)  

  • Dizziness   
  • Low blood pressure   
  • Indigestion (dyspepsia), Bloating of the stomach, Gas, or Burping  
  • Allergic reaction/hypersensitivity (e.g., rash, itching, and eczema) 
  • Reflux, heartburn or GORD a disease caused by stomach acid rising up into your mouth  
  • Hair loss  
  • Fatigue  
  • Injection site reactions (e.g. itching or redness)  
  • Fast pulse  
  • Increased levels of pancreatic enzymes (such as lipase and amylase) in blood  
  • Increased calcitonin levels in blood  
  • Gallstones  

Uncommon  

  • Gallbladder infection, or Cholecystitis 
  • Altered sense of taste  
  • Pain in the Injection site 
  • A delay in the emptying of the stomach 
  • Altered skin sensation 

Who can Access Mounjaro®? UK / Regulatory & Prescribing Context 

NICE guidance on using Mounjaro®: 

The National Institute for Health and Care Excellence, (NICE) their logo in white on a blue background

According to NHS Interim Comissioning Guidance, a patient’s eligibility for Tirzepatide depends on their BMI (Body Mass Index). If the patient’s BMI exceeds 40 kg/m2 or more, the patient meets a step in the eligibility criteria. Patients also need to meet four or more of the following weight-related health conditions: 

  • High blood pressure 
  • Dyslipidaemia (abnormal blood fats) 
  • Obstructive sleep apnoea 
  • Cardiovascular disease (for example, heart disease) 
  • Type 2 diabetes 

(Please note: As of July 2026, the BMI eligibility will fall to the following range: 35 kg/m2 and 39.9 kg/m2.) 

For non-NHS patients, NICE states the following:  

Tirzepatide can only be recommended as an option for managing weight and obesity when used alongside a reduced-calorie diet and increased physical activity plan for adults. Additionally, the following conditions need to be met: 

  • The patient must have an initial body mass index (BMI) of at least 35 kg/m2  
  • At least one single weight-related comorbidity 
  • The company who provides Tirzepatide follows the commercial arrangement 

Additionally, when administering Tirzepatide, it is recommended that you utilise a lower BMI threshold (usually reduced by 2.5 kg/m2) for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean ethnic backgrounds. 

If the patient has lost under 5% of their starting weight after half a year on their highest tolerated dose, the treatment plan should be re-evaluated, and it should be decided whether the patient should continue their treatment. This evaluation should take into account the benefits and risks of treatment for the patient. 

NICE page on Tirzepatide (Mounjaro®) 

Conclusion 

In many cases, Tirzepatide can assist in weight management alongside exercise and a reduced-calorie diet. However, there are strict conditions to its use, including patient monitoring throughout their course of Tirzepatide. As the studies surrounding this medicine continue to develop, so will guidance regarding its usage. If you prescribe Tirzepatide for weight loss, or refer patients to specialists, please ensure you are always up-to-date on the latest guidance regarding the use of Tirzepatide.