Mounjaro weight loss injections - what you need to know

Injecting weight loss pen

Mounjaro is the most recent injectable to be approved by the MHRA for weight loss[1] here in the UK.

Currently used by type 2 diabetics to help improve their blood sugar (glucose) levels, those who are overweight with weight-related health problems will soon be able to access Mounjaro to lose weight, alongside a reduced-calorie diet and increased physical activity.

When a new weight loss drug is authorised, it not only gives patients more choice when it comes to choosing their weight loss treatment, but a lot of potential confusion and questions, too.

How does Mounjaro work? Does it cause any side effects? And, what you’re most likely wondering, how effective is it?

This is your one-stop guide to Mounjaro and its active ingredient, tirzepatide. We’ll answer those all-important questions, so that when Mounjaro is released, you’re fully prepared and confident in your treatment plan.

Tirzepatide – the active ingredient in Mounjaro

Tirzepatide is the active ingredient in Mounjaro. It’s a type of drug known as a GIP/GLP-1 receptor agonist, and it helps you to lose weight by suppressing your appetite.

It works in the same way as Novo Nordisk's[2] other weight loss injectable, semaglutide (known by its brand names Ozempic and Wegovy), does. As you will feel fuller for longer, you will experience fewer food cravings, and by reducing your food intake, it will help you to lose weight.

However, you still have to put the work in by eating the right foods and exercising alongside your treatment plan.

Who makes tirzepatide?

Mounjaro and its active ingredient tirzepatide are made by the pharmaceutical company Eli Lilly[3].

Their medicine portfolio[4] covers diabetes, immunology, neuroscience, oncology, and as of 2023, they’re branching into the weight loss sector, with the MHRA approving the usage of Mounjaro to treat type 2 diabetes and adults with obesity.

GLP-1 and GIP receptor agonists explained

GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) receptor agonists are types of medication that play an essential role in the management of type 2 diabetes and obesity.

They copy the effects of hormones we already have in the body called GLP-1 and GIP, which are released after eating. It boosts insulin release, lowers glucagon levels and slows down digestion, helping to control blood sugar and keep you feeling fuller for longer.

These benefits are why tirzepatide is effective for managing both type 2 diabetes and the treatment of obesity.

Weight loss

Mounjaro helps you lose weight by making you feel fuller for longer and slowing down how quickly your body processes food. This happens because Mounjaro is designed to mimic certain hormones in your body, like GIP and GLP-1, which naturally help to control your appetite and energy use.

When you use Mounjaro, it decreases how much you want to eat by its action on hunger centres in the hypothalamus, an area of the brain that controls appetite.

Additionally, Mounjaro slows down the movement of food from your stomach to your intestines, making you feel fuller faster and for a more extended period, so you end up eating less.


Mounjaro copies the actions of two important hormones, GLP-1 and GIP, found in different parts of the gut. Together, these hormones stimulate insulin release after meals, helping the body manage glucose (sugar) more effectively, especially in people with type 2 diabetes.

When you have type 2 diabetes, the body struggles to handle insulin properly, leading to high blood sugar levels. These drugs mimic and activate GIP and GLP-1 receptors in various organs, addressing insulin issues and aiding in glucose control.

Woman making healthy meal

How Mounjaro is administered

Mounjaro comes in a disposable, multi-dose, single-patient-use, pre-filled pen. 1 pen contains enough for 4 doses, 1 dose taken weekly. This means that you will need 1 pen per month. It’s administered once a week by injecting it just under the skin (subcutaneously). You can inject at any time of the day, with or without food, but how often you take Mounjaro will remain the same.

You or someone else can give the injection, targeting either the stomach (abdomen), thigh or upper arm, but you should rotate the area each time you inject.

The dosage path

Mounjaro comes in the following doses:

  • 2.5mg
  • 5mg
  • 7.5mg
  • 10mg
  • 12.5mg
  • 15mg

You will start with a 2.5mg injection of Mounjaro once a week for the first month. After 4 weeks, you can increase to a 5mg injection once a week. If your prescriber thinks it’s needed, they may choose to increase your dosage by 2.5mg every 4 weeks.

This would bring your dosage up to 7.5mg once a week, then 10mg, 12.5mg, and up to a maximum dose of 15mg. It’s important to note that not everyone will need to use the higher doses in order for Mounjaro to be effective.

Gradually increasing your doses is known as titration, and it helps your body to adjust to the medicine over a period of time. This can prevent you from experiencing side effects, or it lowers the severity of side effects.

Weight loss results

The effectiveness of Mounjaro for weight loss varies from person to person, but the results are considered positive.

A study[5] shows that within the first year of using tirzepatide, 42.3% of individuals experienced a weight loss of at least 15%. In comparison, only 19.3% of patients taking semaglutide, the primary ingredient in Wegovy and Ozempic, achieved a similar level of weight loss.

When factoring in individual risk factors, patients using Mounjaro had a 76% higher likelihood of losing a minimum of 5% of their body weight.

Common side effects

Like all medicines, Mounjaro may cause side effects in some people, but not everyone will experience them. If you’re concerned about any potential side effects, you should speak to your healthcare provider for advice. Common side effects of Mounjaro include:

Some side effects, like nausea, vomiting and diarrhoea, are more likely to occur when your Mounjaro dose is being increased. Thankfully, they decrease overtime as your body adjusts to the medicine.

Your diet and exercise

While there are no foods that are strictly prohibited while using Mounjaro, it’s best to moderate or avoid specific foods as they may worsen side effects such as gas and bloating.

You could also limit the intake of high carbohydrate and sugary foods, as they could contribute to weight gain. Instead, opt for a diet rich in lean proteins, whole grains, fruits, vegetables, nuts, seeds and water. There are lots of different types of diets that you could choose from.

Boosting your physical activity, especially through muscle-building and strength training exercises, is essential while using Mounjaro to prevent muscle loss. You should also ensure there is enough protein in your diet to maintain muscle. While weight loss can occur without exercise, sustaining it may be more challenging once you stop or reduce the medication.

How to get Mounjaro in the UK

Mounjaro has been approved for weight loss in the UK and will be available in February 2024.

Currently, you’re unable to get Mounjaro through the NHS for weight loss. Private clinics, like ourselves, offer weight management treatments like Mounjaro after a consultation with one of our prescribing pharmacists.

Just answer a series of quick and simple questions and one of our prescribers will be able to see if Mounjaro is the right treatment for you.

Mounjaro isn’t suitable for everyone. In order to be considered for treatment, you have to have a body mass index (BMI) of 30 or more, or a BMI between 27-30 and have weight-related health conditions like prediabetes, high blood pressure, high cholesterol or cardiovascular problems.

How much it costs

The price of Mounjaro with us is currently £189 for the first starting pen of 2.5mg. The price of Wegovy (semaglutide) ranges from £199-299 per pen depending on the dose, so Mounjaro does work out as the cheaper option.

Person standing on scales

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Looking to get your weight loss journey started? Why not browse our range of weight management treatments and complete a short and simple consultation today.

One of our helpful prescribers will take a look at your answers to decide which medication is right for you. Once you’re both happy, we’ll deliver your treatment discreetly to your door.

Alexandra Moses - Medical Content Writer
James O'Loan - CEO & Superintendent Pharmacist
James O'Loan , CEO & Superintendent Pharmacist on 14 February 2024
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