A pharmacist has issued a warning to women taking GLP-1 medications such as Mounjaro, saying it could potentially impact the effectiveness of the contraceptive pill.
The Medicines and Healthcare products Regulatory Agency (MHRA) has previously said GLP-1 weight-loss treatments might reduce the efficacy of contraceptive pills due to improper absorption caused by common medication side-effects like vomiting and diarrhoea, and because they slow down stomach emptying. The MHRA has also expressed uncertainty about whether these medicines could harm an unborn child.
As many women are starting or adjusting their weight-loss injections in the lead-up to Christmas or planning to start in January, pharmacists are now warning that festive disruptions could heighten the risk of unplanned pregnancies. They highlight that changes in routines, missed contraceptive pills, dose increases, and common side effects such as vomiting or diarrhoea can all diminish the reliability of the pill, "particularly for those using GLP-1 medications like Mounjaro".
Weight-loss injection specialists at Chemist4U are encouraging women to seek professional medical advice before commencing treatment, reports Chronicle Live, and to contemplate using additional or alternative contraception to remain protected throughout the festive season.
James O'Loan, superintendent pharmacist and weight loss injection expert at Chemist4U, said: "It's critical that people understand how to access and use GLP-1 medications like Mounjaro safely."
He added: "It's important to know that Mounjaro can slow down how your body absorbs medicines taken by mouth, including the contraceptive pill. This means the pill might not protect you from pregnancy as reliably as usual. To stay safe, you should use an extra method of contraception, like condoms, for at least four weeks after starting Mounjaro or if your dose increases. Alternatively, you might want to consider switching to a non-pill or non–oral method."
James advised anyone applying for GLP-1 medication to only do so via NHS services, licensed pharmacies or regulated private clinics and urged everyone to "avoid all online sellers that are not UK registered as not only do many sell unsafe and counterfeit drugs but you won’t receive the proper medical guidance".
He added: “When you apply through NHS services or licensed pharmacies, you’ll have a consultation where the medication and its side effects are explained. You’ll also be asked about any current medications, as it's important to know that Mounjaro can slow down how your body absorbs medicines taken by mouth, including the contraceptive pill."
Contraceptive methods not affected by GLP-1 medications
Both the MHRA and pharmacists advise that individuals using Mounjaro or other GLP-1 medications whilst taking oral contraceptives should additionally use condoms for four weeks after commencing the medication, or consider switching to alternative methods such as the coil or implant. James explained: "Each method has its pros and cons, and what's right for one person might not suit another. We understand this might feel like a hassle, but it's the best way to ensure you're fully protected."
What about other GLP-1 medications?
Mounjaro isn't the sole licensed GLP-1 medication available. In the UK, several licensed GLP-1 medicines are accessible, including semaglutide (marketed under brand names such as Wegovy and Rybelsus), tirzepatide (Mounjaro) and liraglutide (available under various brand names). James noted that Wegovy "doesn't interfere with how the pill works" and "you can continue taking your usual contraceptive pill without needing extra precautions" since it doesn't "directly interact with how the pill works in your body".
What does the UK regulator say?
The Medicines and Healthcare products Regulatory Agency says: "All individuals of child-bearing potential (who are able to become pregnant) using GLP-1 medications should take steps to ensure they do not become pregnant. If you are using Mounjaro (tirzepatide) and take an oral contraceptive (the pill), you should add a non-oral barrier form of contraception (eg condom) for four weeks after starting GLP-1 medicines, and for four weeks after any increase in dose. This is because GLP-1 medicines may reduce the effectiveness of oral contraceptives in those who are overweight or obese."
It adds: "GLP-1 medicines should not be taken during pregnancy or just before trying to get pregnant. This is because there is not enough safety data to know whether taking a GLP-1 medicine can cause harm to the baby."
