You may have heard of the drugs Mounjaro and Zepbound in reference to weight loss medication. They’re both manufactured by Eli Lilly and both have the same active ingredient - tirzepatide. So what’s the difference between them? Is there a difference at all? Read on to find out.

Tirzepatide - the active ingredient in Mounjaro and Zepbound

Mounjaro and Zepbound both share tirzepatide as their active ingredient. This makes them both GLP-1 receptor agonists, similar to other medications like Wegovy (which has semaglutide as its active ingredient). The main difference between tirzepatide and semaglutide is that tirzepatide is also a GIP receptor agonist (GIP stands for glucose-dependent insulinotropic polypeptide). This means it ‘tricks’ your brain into producing GIP. 

GIP is a hormone that’s naturally produced by your small intestine after eating. It stimulates insulin production and increases your insulin sensitivity. Since insulin is one of the hormones involved in appetite control, this is what makes GIP-1 receptor agonists like tirzepatide effective in reducing hunger and managing weight.

What’s the difference between Mounjaro and Zepbound?

Mounjaro and Zepbound are essentially brand names for exactly the same drug - tirzepatide - so there really isn’t much difference aside from the name.

The main difference is in their original use cases. Zepbound is intended primarily as a treatment for obesity, whereas Mounjaro was originally approved for treatment of Type 2 diabetes due to its ability to lower HbA1c. However, since the MHRA authorised it for weight management in 2023, Mounjaro can also be prescribed to treat obesity in the UK.

Zepbound has been approved by the FDA (Food and Drug Administration) in the United States, but only Mounjaro has UK MHRA approval, so you’re only likely to find Mounjaro for sale in the UK for now.