Expert warns these five things can make contraception less effective

Reports of pregnancies in women using weight-loss injections, including those using contraception, have prompted concern from the UK’s Medicines and Healthcare products Regulatory Agency (MHRA).

The MHRA has received over 40 reports of pregnancies among women using weight-loss medications. Data shared with the PA news agency also reveals 26 pregnancy-related reports specifically for the Mounjaro jab. This has led to online discussions about so-called "Ozempic babies".

The MHRA advises that Mounjaro may reduce the effectiveness of oral contraceptives in overweight individuals. Patients taking Mounjaro are recommended to use condoms, especially in the first four weeks of starting the medication and after any dose increase.

The agency also stresses “skinny jabs” such as Ozempic, Wegovy, Saxenda, Victoza, and Mounjaro should not be used during pregnancy, when trying to conceive, or while breastfeeding.

In some cases, women are also advised to continue using contraception for up to two months between stopping the medicine and trying to get pregnant.

This guidance around pregnancy is included in patient information leaflets given to people who are accessing the skinny jabs from regulated sellers like pharmacies.

In light of this news, we got in touch with Dr Alisha Esmail, women’s health GP at London Gynaecology, to find out what other factors may influence hormonal contraception’s effectiveness…

Vomiting within a few hours of taking a contraception pill can reduce its effectiveness, says Esmail.

“If you’re sick – especially with vomiting or diarrhoea – soon after taking your pill, your body might not absorb it properly, which can lower the hormone levels needed for it to work properly,” she explains. “Remember, this applies to the morning-after pill too, which is especially time-sensitive.

“If you’ve been unwell, it’s a good idea to use back-up contraception and check in with a clinician – they can help work out if you need to take another dose or consider a different option.”

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Weight can also play a role in how well some hormonal contraceptives work.

“For instance, the patch and emergency contraception might be a little less effective if you have a higher Body Mass Index (BMI),” says Esmail. “This is because your body may absorb and process the hormones differently, although for most people the difference is quite small.

“Because of this, doctors often recommend exploring other methods to ensure you get the most reliable protection. Safety is key – some combined hormonal options (those with both oestrogen and progesterone) may carry a slightly higher risk of side effects for people with higher BMI, so it’s always a good idea to discuss your personal health and preferences with your clinician.”

Some medications can lessen the effectiveness of hormonal contraceptives, so it’s important to talk to a clinician if you’re unsure how your medication might affect them.

“Some medications like certain antibiotics (e.g. Rifampicin), anti-seizure drugs, HIV medications, and even herbal supplements like St. John’s Wort can reduce the effectiveness of hormonal contraceptives,” highlights Esmail. “They may speed up how quickly hormones are digested in the liver, lowering your blood hormone levels and reducing its reliability.

“So, it’s definitely worth letting your clinician know about any medications you’re taking – whether they’re prescribed or not.”

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Incorrect use is one of the main reasons why contraception can fail.

“Some of the most common slip-ups I hear about include forgetting pills, not taking them at the same time each day, starting a new pack late, or incorrect use of patches, rings, or injections,” says Esmail. “With methods like the pill, consistency is key – even small drops in hormone levels can allow ovulation, increasing your risk of an unexpected pregnancy.

“If sticking to a routine is proving tricky, it’s worth knowing there are plenty of longer-acting options that don’t rely on daily habits – you’ve got choices.”

The GP also points out that pill packs include a leaflet with a section on missed pill rules, which can be helpful when you’re uncertain about what to do. She also reinforces the importance of timing when it comes to emergency contraception, such as Plan B.

“And when it comes to emergency contraception, timing really matters – the sooner it’s taken after unprotected sex, the more effective it is,” says Esmail. “Delays can reduce its chances of working, so don’t wait to seek advice if you think you might need it.”

The GP also recommends storing contraception pills at room temperature or cooler because if too hot the hormones within them could be changed/ deactivated.

“Storing your pills in a place that gets too hot – like a car on a sunny day – can affect how well they work,” says Esmail.