How Weight Loss Injections Can Affect Contraception

Over the past few years, the demand for weight loss injections such as Wegovy (semaglutide), and Mounjaro (tirzepatide) have grown exponentially throughout the UK. With 1.5 million people across the UK using a GLP-1 medication as of March 2025. These once-weekly injections are helping thousands of people lose weight safely and sustainably under medical supervision and advice. But, for those who may be, or become pregnant, it’s important to understand how these medications can affect fertility, and contraception.

How GLP-1 Medications Work

Wegovy, Liraglutide, and Mounjaro are all examples of GLP-1 receptor agnostic medications. These work by mimicking the hormones which regulate appetite and blood sugar levels. Making you feel full for longer, and delaying that hunger trigger in the brain, people can better manage their calorie intake. These medications also work by slowing stomach emptying, meaning that you feel full for longer. Yet, while these effects support weight loss, they can also influence how other oral medications are absorbed, including the contraceptive pill.

Why Women on the Pill Should Take Extra Care

Guidance from the MHRA (Medicines and Healthcare Regulatory Agency) has stated that women using oral contraception should take added precaution when using GLP-1 medications. Especially if using Mounjaro (tirzepatide).

This is because the delayed stomach-emptying effect of the pens can cause the contraceptive pill to be absorbed more slowly. In some cases, it may not be absorbed at all. Moreover, if patients are suffering from side effects such as vomiting or diarrhoea (common side effects during the earlier days of injecting), this can certainly reduce the effectiveness of the pill, raising the risk of unintended pregnancy.

For this reason, we recommend, that those who are taking this medication opt for other forms of contraception either, as well, or instead of the pill. Using additional forms of contraception such as the barrier method (e.g. condoms) when beginning GLP-1 treatment or after each dose change. Or considering a non-oral contraceptive such as the implant, IUD, patch etc. for continued protection.

While other GLP-1 medications seem to have less impact on absorption, the same general precautions still apply. This is especially important if you experience digestive side effects.

Weight Loss and Fertility

For some, significant weight loss achieved using these medications can increase or even restore natural fertility. Especially if they had been experiencing irregular ovulation due to obesity or PCOS.

Several UK clinics have already discovered an increase in ‘surprise pregnancies’ after patient has lost weight using GLP-1 medications. Even amongst those who had previously struggled to conceive.

Yet, because Wegovy, Mounjaro, and Nevolat are not recommended during pregnancy or breastfeeding, treatment should be stopped well before planned conception for those wishing to get pregnancy.

What About Men?

For men, there is no worry about GLP-1 injections affecting contraception or harming a developing foetus. These medications do not affect sperm, and there is currently no evidence to suggest that that they pose any reproductive risk to men.

However, as with women who have seen in increase if fertility as a byproduct the weight loss and blood sugar control in these medications; the same can be found with men. Improved weight and glucose control can sometimes enhance male fertility too and improve testosterone balance.

So, while men benefit from the same fertility benefits found from this treatment, they do not have the same contraception concerns.

Across the UK, weight loss injections are transforming weight management for thousands of people. But it’s important to stay informed about how they may interact with other aspects of our health. If you’re sexually active and not wishing to conceive, it’s important to take the right precautions. This can help you avoid unwanted pregnancy. It also allows you to use these medications safely and confidently.