GLP-1 medicines, contraception and planning a pregnancy

There is not enough reliable human data to show that these medicines are safe in pregnancy, and animal studies have shown harm at some doses. Weight loss during pregnancy is also not advised, because it can limit the nutrients and energy a developing baby needs. For those reasons product information recommends stopping treatment before trying to conceive. The interval varies by product, so the prescriber or the leaflet should be your guide rather than a general rule.

The MHRA has drawn attention to the possibility that tirzepatide slows stomach emptying in a way that could reduce the absorption of oral contraceptive pills, particularly after starting and after each dose increase. The advice has been to consider using a barrier method alongside, or switching to a method that does not depend on absorption through the gut. Vomiting and severe diarrhoea can also reduce pill effectiveness whatever medicine is involved.

Longer-acting methods such as the intrauterine device, the intrauterine system, the implant and the injectable do not depend on the gut. A prescriber, GP or sexual-health clinic can talk through which suits you.

• Tell your prescriber which contraceptive you use before starting.

• If you use a pill, ask what extra precautions apply and for how long.

• Remember vomiting and diarrhoea can reduce pill effectiveness.

• Consider a method that is not affected by gut absorption.

Excess weight can interfere with ovulation, particularly in polycystic ovary syndrome. When weight falls, ovulation may resume. People who have been told that pregnancy is unlikely sometimes conceive unexpectedly. If you do not wish to become pregnant, do not rely on irregular cycles for protection.

If you are hoping to conceive, tell your prescriber early. Together you can plan when to stop, how to manage weight and, if you have diabetes, glucose control during the gap. Folic acid is recommended before conception and in early pregnancy, and a higher dose is advised for people with obesity or diabetes, which your GP or midwife can confirm. Your care in pregnancy will also take your earlier weight and history into account.

Stop the medicine and contact your GP, midwife or prescriber promptly. Do not panic: most information comes from reports rather than proven harm, and the priority is to review treatment and arrange appropriate antenatal care. If you are taking the medicine for diabetes, your team will help you switch to a treatment suitable in pregnancy rather than stopping glucose treatment altogether.

There is little evidence about transfer into breast milk or effects on infants, so product information and most clinicians advise against use while breastfeeding. Weight management after birth can be approached with nutrition and activity guidance in the meantime. Discuss options with your health visitor or GP.