Recently approved for weight loss in the UK, Mounjaro has hit the headlines as an effective solution for helping people with excess weight or obesity.

In this article, we’ll explain more about this particular medication, how it works, the science backing its efficacy, potential side effects, and who Mounjaro is most suitable for.

This will provide you with sufficient information to make a decision on whether or not Mounjaro weight loss may be right for you. Of course our team of experts at Thriva are here to support you in answering any further questions.

What is Mounjaro?

Mounjaro is the brand name for a drug called tirzepatide, which is produced by US-based pharmaceutical company Eli Lilly. 

It is injected once weekly under the skin of the stomach, thigh, or upper arm.

Originally created as a type II diabetes medication and approved by the US Food and Drug Administration (FDA) in May 2022, it was approved more widely as a weight loss solution by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) in late 2023.

That’s because clinical trials showed that people who do not have diabetes but do have elevated body mass indexes (BMI) lost considerable weight when they used Mounjaro.

How does Mounjaro work for weight loss?

Similarly to other weight loss medications, such as Wegovy, Mounjaro works to reduce appetite and makes you feel more full. 

The medication also slows down the rate at which your stomach empties, contributing to the weight loss process by helping you feel fuller faster and for longer.

At the physiological level, Mounjaro activates receptors in the body for GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide), which are natural hormones that influence blood glucose levels. Activating these receptors sends signals to the areas of the brain that control appetite, telling us we feel full.

Mounjaro is a unique and exciting medication because it’s the only one available that has this dual mechanism affecting both GLP-1 and GIP. Combined GIP and GLP-1 agonists can help promote more effective weight loss than GLP-1 agonists alone (such as semaglutide).

Mounjaro is not a silver bullet

Here at Thriva we hold ourselves to the highest clinical standards. We think it's important to know that medication like Mounjaro is not a silver bullet. 

Mounjaro can be a powerful tool for weight loss. However, it's just as important that you combine the medication with lifestyle change - eating a high quality diet with plenty of protein, and exercising regularly. Strength training is particularly important to ensure you don't lose too much lean muscle mass whilst losing weight.

Medications like Mounjaro can help to reduce the cognitive burden of dieting, so that you can focus more on other lifestyle changes.

Thriva's medication-supported weight loss programme will support you to make these changes and achieve sustainable improvements to your health. 

What are the side effects of Mounjaro?

The most common Mounjaro side effects in clinical trials included nausea, diarrhoea, decreased appetite, vomiting, constipation, indigestion, and stomach pain.

In a 2023 comparative study of Mounjaro with the weight loss drug Mounjaro, nausea and vomiting were reported for about 1 in 5 people with each of the medications. Gallstones were reported for roughly 1 in 6. 

The manufacturers also warn that Mounjaro may cause serious side effects, including inflammation of the pancreas, low blood sugar, serious allergic reactions, kidney problems, stomach problems, and changes in vision. 

Patients are advised to stop using Mounjaro immediately in the event of serious symptoms, such as severe stomach pains or a strong allergic reaction, and to seek medical attention.

Who can use Mounjaro?

Mounjaro is appropriate for adults who have been diagnosed with type II diabetes, or are struggling with obesity/being heavily overweight. 

While people can control their type II diabetes or lose a great deal of weight with Mounjaro, there is a likelihood that the weight lost will be regained if the medication is discontinued.

This means that if unhealthy choices are still made, such as consistently eating an unhealthy diet, making no efforts to exercise, or not managing stress, then weight gain following a period of taking Mounjaro is highly probable.

You should not use Mounjaro if you:

  • Discover you are allergic to it.
  • Have personal or family history of medullary thyroid carcinoma (a type of thyroid cancer).
  • Multiple endocrine neoplasia type 2 (tumours in your glands).

Also, tell your doctor if you have ever had:

  • Pancreas problems.
  • Kidney disease.
  • Any severe stomach problems such as problems with digesting food or slowed emptying of your stomach.
  • Diabetic retinopathy (a diabetes complication that affects the eyes).

Tell your doctor if you are pregnant or plan to become pregnant. It is not known if Mounjaro will harm an unborn baby. Also, Mounjaro can make birth control pills less effective.

Comparison of Mounjaro with Wegovy

While Mounjaro and Wegovy are similar medications in the way that they work, they aren’t quite the same.

The active ingredient in Mounjaro is tirzepatide, while the key compound in Wegovy is semaglutide. 

Mode of action - Mounjaro vs. Wegovy

Both medications belong to the GLP-1 agonist drug class, with each supporting weight loss by reducing appetite. 

GLP-1 is a hormone which reduces hunger and food seeking behaviours by communicating with the hypothalamus – the part of the brain which controls appetite.

The main difference is that Mounjaro also mimics GIP, which plays an important role in glucose metabolism and helps to regulate body weight.

Dosage of Mounjaro vs Wegovy

Both are administered once per week by injection. The commencement dose for Mounjaro is suggested at 2.5 mg per week, whereas Wegovy is advised to start at a dose of 0.25 mg weekly.

Over time, the dosage of both these medications is progressively increased based on individual response and tolerance.

Efficacy of Mounjaro vs Wegovy

In the first of its two obesity phase 3 trials, Mounjaro delivered a weight reduction of up to 21% in non-diabetic patients. By comparison, Wegovy showed an average weight loss of 15% – or a 12.4% difference from placebo – in its own trial in patients without diabetes. 

Side effects of Mounjaro vs Wegovy

Manufacturers of Mounjaro (Eli Lilly) and Wegovy (Novo Nordisk) have detailed the most common side effects on their website. Experts believe that the side effects from Mounjaro may be stronger, due to the hormonal action of the medication being more intense. Side effects can vary significantly from person to person. 

Wegovy: Nausea, diarrhoea, vomiting, constipation, stomach pain, headache, tiredness, upset stomach, dizziness, feeling bloated, belching, gas, stomach flu, heartburn, runny nose or sore throat.

Mounjaro: nausea, diarrhoea, vomiting, decreased appetite, constipation, indigestion, and stomach pain.


Positive lifestyle changes, such as more exercise and eating healthier foods, should always be seen as a priority and a first step when it comes to weight loss. However, we fully understand that your health journey is not always that straightforward. 

There are frequently other factors to consider - and weight loss medications, such as Mounjaro, have emerged as a viable, proven solution for those struggling with their weight.

Mounjaro’s impressive results in delivering 15-20% weight loss – and the fact that it is very effective in suppressing appetite – make it a very useful option for many people who have struggled to lose weight by other means.

However, expert support is absolutely essential. Thriva's unique medication-supported weight loss programme combines this type of medication with expert medical support and blood testing to track health progress.

Research Links

Tirzepatide (Mounjaro) demonstrated significant and superior weight loss compared to placebo in two pivotal studies

Comparative Effectiveness of Semaglutide and Tirzepatide for Weight Loss in Adults with Overweight and Obesity in the US: A Real-World Evidence Study