What is Tirzepatide?

Tirzepatide, pronounced ‘ter-ZEP-uh-tide’, is a glucagon-like peptide-1 (GLP-1) receptor agonist.

Tirzepatide is the name of the drug in Mounjaro weight loss injections. Mounjaro is the UK brand name. In the US, it is also known as Zepbound.

It's normal for medicines to have multiple names, including the drug name, which represents its active ingredient, and a brand name selected by the manufacturer for marketing. The brand name is often easier to pronounce than the drug name, but not always!

Mounjaro injections are manufactured by Eli Lilly, a pharmaceutical company whose head office is based in the US.

What is Tirzepatide used for?

Tirzepatide UK is sold under the brand name Mounjaro, and it is used to help people who meet specific criteria lose weight.

Tirzepatide Mounjaro injections are used by adults over 18 who have a BMI of over 30 or 27 with weight-related comorbidities such as type-2 diabetes.

To achieve the best results, tirzepatide weight loss medication must be used in conjunction with a healthy diet and exercise routine.

Does Tirzepatide work?

Yes, in fact, Mounjaro Tirzepatide injections have recently taken the weight loss world by storm. They are more effective and produce better results than their predecessors, such as Wegovy and Saxenda.

A 2023 study on treatment with Tirzepatide for weight loss, the overall mean weight reduction over 88 weeks of treatment was 25.3% for Tirzepatide and 9.9% for placebo, although this was a relatively small sample group.

The manufacturer Eli Lilly also published a news release in 2022 showing that their SURMOUNT-1 clinical trial with Tirzepatide (5 mg, 10 mg, 15 mg) achieved superior weight loss compared to placebo at 72 weeks of treatment, with participants losing up to 22.5% of their starting weight.

How does Tirzepatide work for weight loss?

Tirzepatide UK works for weight loss in two different ways, compared to only one way with similar weight loss treatments like Wegovy and Ozempic:

1. By making you feel fuller for longer after eating
2. By breaking down fat stores for energy instead of using the food you eat

Tirzepatide is a dual GIP and GLP-1 receptor agonist.

Tirzepatide mimics the hormone GLP-1, which regulates hunger and helps people eat less food.

It also mimics the GIP hormone. This hormone is known for increasing the amount of glucose in the body, which can lead to a feeling of fullness.

Tirzepatide delays emptying food from the stomach into the intestines, prolonging the sensation of satisfaction and fullness.

Tirzepatide may boost energy levels, encouraging more frequent movement during the day and increasing calorie burn.

Tirzepatide dosage

Tirzepatide Mounjaro injections are available in the following strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.

With tirzepatide, the strength of the doses must be gradually increased to allow your body to get used to the medicine. This will reduce the chance of side effects.

When starting weight loss treatment with tirzepatide injections, you must start on the lowest dose, which is 2.5mg. You can then decide to increase your dose no sooner than 4 weeks at a time, you must stick to the following dose chart when increasing your dose:

Weeks 1 - 4: Mounjaro (tirzepatide) 2.5mg

Weeks 5 - 8: Mounjaro (tirzepatide) 5mg - you can stay on this strength if you are still losing weight

Weeks 9 - 12: Mounjaro (tirzepatide) 7.5mg

Weeks 13 - 16: Mounjaro (tirzepatide) 10mg - you can stay on this strength if you are still losing weight

Weeks 17 - 20: Mounjaro (tirzepatide) 12.5mg

Weeks 21+: Mounjaro (tirzepatide) 15mg - you can stay on this strength if you are still losing weight

These increases are made every four weeks. The maximum dosage is 15 mg once weekly.

For more detailed information on Mounjaro (Tirzepatide) dosing, see our Mounjaro dosage guide for weight loss here.

Tirzepatide side effects

Side effects are possible with any medicine; this is also true with Mounjaro Tirzepatide injection. While the side effects are mild, they can be annoying, especially with the most common Mounjaro side effects being gastrointestinal issues such as nausea and diarrhoea.

Before taking any medicine, you should familiarise yourself with the side effects and consider whether the treatment's benefits outweigh the potential side effects.

Tirzepatide side effects include:

Common Tirzepatide side effects (1 in 10 people):

• Nausea
• Decreased appetite
• Diarrhoea

Other side effects, although less common than the above, could include:

• Vomiting
• Acid reflux
• Constipation

This is not a complete list of Tirzepatide Mounjaro side effects. For the full list, refer to the Mounjaro patient information leaflet.

Tirzepatide alternatives

Tirzepatide injections like Mounjaro are not the only weight loss injections available in the UK.

Semaglutide injections, brand name Wegovy, are also available for weight loss.

Semaglutide is also available under the brand Ozempic; however, this medicine is only licensed to be used by people with type-2 diabetes.

Tirzepatide vs Semaglutide

As the table above shows, Wegovy and Mounjaro injections have very similar dosages and common side effects.

Tirzepatide (Mounjaro) injections offer superior weight loss results with a loss of up to 22.5% compared to up to 17% with semaglutide (Wegovy) injections.

You can find a more detailed comparison of the differences in our dedicated Mounjaro vs Wegovy article here.

Tirzepatide UK price

You can get Tirzepatide weight loss injections from Oxford Online Pharmacy as the brand name Mounjaro UK.

The cost of Mounjaro weight loss injections starts from £129.99 for 4 weeks' worth of treatment.

*These prices are as of 20.02.2025 and are subject to change.

FAQs

How long does it take for Tirzepatide to suppress appetite?

This can vary from person to person. While some may notice that their appetite is suppressed in the first month of treatment, it may take a little while for others, meaning that they will not experience the suppression until they increase their dose.

How long does Tirzepatide last in the fridge?

Tirzepatide UK can be kept in the fridge unopened or opened and is safe to use until the expiry date on the box.

Once Tirzepatide injections are stored out of the fridge at room temperature, it should be used within 30 days.

If the pen has been kept out of the fridge for more than 30 days, do not use it.

Is Tirzepatide safe?

Tirzepatide injections such as Mounjaro UK are generally considered safe as long as you use them as prescribed by your doctor. These injections are licensed to treat weight loss and have had years of testing to ensure they’re safe for human use.

Being on other medicines or having underlying conditions can affect whether a person can use them or not, so it is extremely important to inform your doctor before starting treatment.

References:

1. Here's How Much Weight People Regain After Stopping Mounjaro, Zepbound, Health Line
2. Lilly's tirzepatide delivered up to 22.5% weight loss in adults with obesity or overweight in SURMOUNT-1, Eli Lilly and Company
3. Tirzepatide, a dual GIP/GLP-1 receptor co-agonist for the treatment of type 2 diabetes with unmatched effectiveness regarding glycaemic control and body weight reduction, PubMed
4. What is Mounjaro and how does it work?, Diabetes.org
5. Tirzepatide - StatPearls,  NCBI Bookshelf