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Mounjaro: Uses, How It Works & Side Effects

Dr Roger Henderson
Reviewed by Roger HendersonReviewed on 29.04.2024 | 5 minutes read

Mounjaro is the brand name for a new class of drug called a GIP and GLP-1 receptor agonist. It is designed to lower blood sugar levels in the body in adults with type 2 diabetes when combined with regular exercise and dieting. GIP is short for glucose-dependent insulinotropic polypeptide, and GLP-1 stands for glucagon-like peptide-1, both of which belong to a type of body hormone known as incretins which help to regulate blood sugar.

Some people who take Mounjaro may also lose weight because of its effect on the body. Although it is not approved as a weight loss drug, doctors may prescribe it ‘off label’ (when an approved drug is used for a purpose other than the one it has been approved for).

How does Mounjaro work?

By imitating the effect of the incretin hormones GIP and GLP-1 in the body, Mounjaro activates certain receptors in the body linked to these, and as a result lowers blood sugar levels. It does this in three main ways:

  • Making your body extra sensitive to the sugar-regulating hormone insulin

  • Making your pancreas gland (where insulin is made) release more insulin after a meal

  • Stopping your liver from making additional sugar

It also slows down the speed at which food passes through your stomach after a meal, which can make you feel full for longer than normal.

If you have type 2 diabetes and take other medication for this condition, Mounjaro is used:

  • By itself if you are unable to take metformin

  • With metformin

  • With metformin and a sulfonylurea

  • With metformin and a sodium-glucose cotransporter 2 inhibitor (SGLT2i)

  • With basal insulin (with or without metformin)

How to use Mounjaro

Mounjaro is a drug that you inject subcutaneously (under the skin) once a week. It comes in single-dose prefilled pens, and you will be shown how to use these by a healthcare professional. The drug also comes with step-by-step instructions and there are also instructional videos available online.

Mounjaro is injected into the abdomen or thigh (or the upper arm if someone else is giving it to you). A different injection site should be used every week, as using the same place all the time can cause irritation in that area. If you also use insulin, Mounjaro and insulin can both be given at the same time as long as they are not both given in exactly the same spot - give them a few centimetres apart.

What are possible side effects of Mounjaro?

Mild side effects

The most common side effects when using Mounjaro are linked to the digestive system, such as nausea and vomiting, diarrhoea, abdominal pain, constipation or heartburn. There may also be mild reactions at the injection site or mild allergic reactions.

Most of these mild side effects typically settle within a few days to a fortnight. If they do not, discuss them with your doctor.

Serious side effects

These are uncommon but may occur and include:

  • Acute pancreatitis (inflammation of the pancreas gland)

  • Low blood sugar levels (hypoglycaemia)

  • Gallbladder problems such as gallstones

  • Severe vomiting and diarrhoea

  • Severe allergic reactions

  • An increased risk of thyroid cancer

To help avoid side effects, talk to your doctor before you take Mounjaro especially if you have:

  • type 1 diabetes

  • any heart condition that causes an increase in your heart rate

  • ever experienced severe allergic reactions when taking a GLP-1 receptor agonist medicine

  • ever had diabetic ketoacidosis (increased ketones in the blood or urine)

  • severe problems with your stomach (gastroparesis) or food digestion

Who is Mounjaro for?

Mounjaro is designed for use in people with type 2 diabetes, in addition to diet and exercise, in order to help manage blood sugar levels. It is not designed for use in type 1 diabetes.

Mounjaro should <u>not</u> be used if:

  • you are allergic to tirzepatide or to any ingredient in Mounjaro

  • you, or a member of your family, has ever had Medullary Thyroid Cancer (MTC)

  • you have Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)

  • you are pregnant or breast-feeding

It is not recommended for use under the age of 18 years.

Can Mounjaro be prescribed for weight loss?

Yes, it may be prescribed for weight loss because of its effect on the body, although it is not approved as a weight loss drug as such. However, doctors are able to prescribe it ‘off label’ (when an approved drug is used for a purpose other than the one it has been approved for) as an aid to help with weight loss.

If you’re overweight or obese, losing weight may lower your blood sugar level and so make diabetes easier to manage. Reaching and maintaining a weight that’s healthy for you may also slow down the progression of diabetes.

Clinical studies suggest that obese people with type 2 diabetes who used Mounjaro for 72 weeks could lose up to 15% of their body weight in that time.

Mounjaro and diet

Mounjaro should be used along with a healthy diet, appropriate for anyone with type 2 diabetes. If nausea is a side effect, avoid high-fat foods and eat small frequent meals rather than three main meals each day. Always stop eating when you feel full, and consider eating blander foods if nausea remains a problem.

Where do I obtain Mounjaro?

Mounjaro is licensed by the Medicines and Healthcare Products Regulatory Agency (MHRA) for sale in the UK. The NHS is legally obliged to fund and resource medicines and treatments recommended by NICE and in September 2023, NICE approved Mounjaro for treating poorly controlled type 2 diabetes (T2D) in adults alongside diet and exercise. This means it can now be made available to NHS patients with poorly controlled type 2 diabetes subject to stock being available.

In the US, the price can be over $1,000 a dose depending on the patient’s insurance plan.

Is Mounjaro the same as Wegovy or Ozempic?

No, it is a completely new class of drug because instead of being a single-receptor agonist, like semaglutide (the drug in Ozempic and Wegovy), Mounjaro activates two receptors at the same time. This is why it is called a ‘dual-agonist’ treatment’. This double agonist approach seems to be the reason why people who use Mounjaro injections lose even more weight than those who use a single-receptor agonist medication.

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Dr Roger Henderson
Reviewed by Roger Henderson
Reviewed on 29.04.2024
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