Mounjaro and metformin: are they safe to take together?

Do you want to use Mounjaro injections for weight loss or to help manage your blood sugar? Are you already taking metformin as a treatment for type 2 diabetes?

If so, you may wonder how the two medications interact. Is it safe to take Mounjaro and metformin at the same time?

The short answer is yes. It's generally considered safe to take Mounjaro and metformin together. However, as with any drug combination, it's important to discuss the treatments with your healthcare provider first to make sure they're right for you.

Let's look at things in a little more detail – starting with the drugs themselves.

What is metformin and how does it work?

Metformin is a type 2 diabetes treatment that helps to lower blood sugar (blood glucose). It's the most common type 2 diabetes treatment prescribed in the UK.

Metformin lowers blood sugar in several ways: 

• It reduces the amount of glucose produced and released into the bloodstream by the liver.
• It slows the absorption of glucose by the intestines.
• It improves the body's sensitivity to insulin. This helps the insulin work more effectively.

For more information on metformin – including common side effects – see the NHS website.

What is Mounjaro and how does it work?

Mounjaro has become well-known as an injectable weight loss medication. However, it was originally developed as a treatment for type 2 diabetes.

Like metformin, it helps to lower and regulate blood sugar. It also helps people with obesity lose weight. That's because it mimics two natural hormones called GLP-1 and GIP.

These hormones trigger insulin production, which encourages your body to use blood sugar for energy. This helps to control food cravings. It also slows down digestion, helping you feel full for longer.

The medication is prescribed as a once-weekly subcutaneous injection. It's supplied as an injection pen containing four doses – so each pen has enough medication for four weeks.

Learn more about our Mounjaro medication programme.

Can metformin and Mounjaro be taken together?

Yes. Mounjaro and metformin are different drugs with different actions. However, they are considered compatible and complementary.

In other words, the two medications tend to work well together. Patients who take Mounjaro and metformin often see improved blood sugar control compared to those taking metformin on its own.

A randomised controlled trial from 2023 saw a group of diabetic patients take metformin alongside Mounjaro for 40 weeks. Researchers noted no severe cases of low blood sugar – and most side effects were similar to those you'd usually expect from a medication like Mounjaro.

Results like these suggest that Mounjaro and metformin are safe and effective when taken together. However, you should always talk to your healthcare provider before starting a new treatment. That's because everyone responds to medications differently. Your doctor needs to make sure that the drug combination is suitable for you.

Can you take Mounjaro instead of metformin?

The National Institute for Health and Care Excellence (NICE) has published guidelines for prescribing Mounjaro. These guidelines say that Mounjaro can be prescribed instead of metformin – but not as a first-line treatment.

In other words, it shouldn't be the first thing doctors consider when treating a person with type 2 diabetes. Mounjaro would only be prescribed on its own or with other anti-diabetic medications, 'when metformin is considered inappropriate due to intolerance or contraindications'. 

Your healthcare provider would make this decision on a case-by-case basis after considering your unique healthcare needs and medical history.

Remember: you should never reduce or stop taking prescribed metformin without talking to your healthcare provider first.

Want to learn more about SemaPen's non-surgical weight loss treatments, including Mounjaro and Wegovy? You'll find lots of helpful information in our expert starter guides.

Sources

1. Gao, L. et al. (2023) "Tirzepatide versus insulin glargine as second-line or third-line therapy in type 2 diabetes in the Asia-Pacific region: the SURPASS-AP-Combo trial" Nature Medicine, 29, 1500–1510 https://doi.org/10.1038/s41591-023-02344-1

This article was reviewed and approved by Qutayba Almerie MD, MSc, FRCS on 14 July 2025.