weight loss

4 minute read

Mounjaro weight loss medication: how it works


Wegovy, Ozempic, Saxenda, Rybelsus…in recent years, a wave of new weight loss medications have been approved to treat obesity in the UK. Mounjaro is the most recent of those, having been approved by the MHRA in November 2023.

But what exactly is it? How does it compare with other weight loss medications? And how effective is it?

Let’s take a look. 

What is Mounjaro?

Mounjaro (pronounced mown-jar-oh) is the brand name of the diabetes and weight loss medication in the UK. You might’ve also come across the term Zepbound, which is the brand name of the weight loss version in the US. They’re the same drug with the same active ingredient - they’re just prescribed for different purposes in different doses.

Mounjaro was originally manufactured as a treatment for type 2 diabetes. But over time, it was discovered that it also helped patients lose weight by feeling fuller for longer - making it an effective treatment for obesity.

After a series of clinical trials, Mounjaro was approved by the MHRA in November 2023 for weight management and weight loss. That means it can now be prescribed to eligible patients in the UK.

Who is eligible for Mounjaro?

A healthcare professional will need to consider several factors to assess your suitability for the treatment. They’ll ask you about your lifestyle, any medications you’re currently taking, and treatment preferences. The consultation can be carried out online.

Mounjaro is a medication that’s specifically prescribed for weight loss. It should never be taken by someone who’s not overweight.

How does Mounjaro work?

Mounjaro contains the active ingredient tirzepatide, which imitates the GLP-1 and GIP hormones in your body. By imitating the GIP hormone, it sends signals through the brain to regulate energy balance. As well as this, by mimicking the GLP-1 hormone, tirzepatide slows digestion, reduces hunger, and combats cravings. The combination of these effects make the dual-acting medication a reliable treatment for reducing appetite, ultimately leading to weight loss. 

It’s worth noting that Mounjaro alone isn’t a suitable treatment for obesity, nor is it a replacement for a healthy lifestyle. It should always be used together with a balanced diet and regular exercise.

How do you take Mounjaro?

You inject Mounjaro yourself once a week, at the same time every week (or as close to the same time as possible). If you’re prescribed Mounjaro then your clinician will guide you through the injection process, although it’s fairly straightforward for most patients.

The name of the device you use to inject Mounjaro is called the KwikPen. The four-dose pen was approved for use by the MHRA in January 2024.

What do the clinical trials say?

More than 10 clinical studies have been carried out on Mounjaro with the majority of these looking at patients with type 2 diabetes. Let’s focus on the study looking at the treatment of obesity:

A 72-week study found that Mounjaro combined with healthy lifestyle choices led to an average 22% weight loss in patients on the highest maintenance dose. The study concluded that the medication ‘provided substantial and sustained reductions in body weight.’

How Mounjaro compares to other weight loss medications


Whilst Mounjaro contains the active ingredient tirzepatide, Wegovy instead contains semaglutide. Both of these ingredients work by regulating your appetite. The main difference between the two medications is that Wegovy mimics a GLP-1 hormone whereas Mounjaro mimics both GLP-1 and GIP hormones.


Ozempic is essentially the same as Wegovy but it’s prescribed for type 2 diabetes instead of obesity. As it’s used to treat a different condition, it comes in different doses.


Semaglutide is also the active ingredient in Rybelsus. It comes in tablet form rather than injection.


Saxenda contains a different active ingredient (liraglutide) to Mounjaro. It’s also a weekly injectable and has been shown to lead to weight loss when combined with a balanced diet and regular exercise.


Instead of suppressing your appetite, Alli (the brand name for the active ingredient orlistat) works by preventing around one-third of the fat you consume from being absorbed. It's an over-the-counter medication.


The two active ingredients in Mysimba are naltrexone and bupropion - substances normally used to treat opioid addiction and help people quit smoking. It’s taken in tablet form rather than injected and also works by regulating your appetite.

The side effects of Mounjaro

The two most common side effects of Mounjaro are nausea and diarrhoea. They have been reported by 12 - 18% of patients. In general, the stronger the dose, the more often these side effects are reported.

These side effects tend to be temporary, and start to subside once your body gets used to the medication. This can sometimes take around two weeks.

To try and minimise adverse reactions, Mounjaro is usually prescribed at a lower dose and then gradually increased while your body adjusts.

The other most common side effects (reported in 5% of patients or more) include:

  • Vomiting

  • Constipation

  • Indigestion

  • Stomach pain

Other less common side effects of Mounjaro (reported by less than 5% of patients) include:

  • Quickened heart rate

  • Redness or swelling around the spot of the injection

  • Skin rashes

  • Eczema

  • Acute gallbladder disease

  • Acute pancreatitis

If you experience any continued side effects from Mounjaro then you should discuss them with your clinician as soon as possible.

The numan take

Clinical trials indicate that Mounjaro effectively supports weight loss in the majority of patients who use it. By regulating appetite and suppressing food cravings, the medication promotes healthy lifestyle choices and sustainable habits that last.