Women using weight-loss jabs have been warned by the UK’s medicines regulator that they must use effective contraception.

The Medicines and Healthcare products Regulatory Agency (MHRA) says it is not known whether taking the medicines, such as Wegovy and Mounjaro, could harm an unborn baby.

It also warns that weight-loss jabs may make the contraceptive pill less likely to work in those who are overweight or obese.

There are concerns that the growing popularity of ‘skinny jabs’ means many women aren’t using the drugs safely or getting the right advice.

It’s thought the contraceptive pill may not be absorbed properly due to common side-effects of the jabs such as vomiting and diarrhoea, and because they slow the emptying of the stomach.

The MHRA says women should use contraception while taking GLP-1 medicines and for a certain period afterwards before trying to become pregnant – two months for Wegovy and Ozempic, and one month for Mounjaro.

It also advises that those using Mounjaro and taking an oral contraceptive should also use a condom for four weeks after starting the drug, or switch to another method such as the coil or implant.

Advice on contraception already appears in patient information leaflets that come with the medicines, but the MHRA has now issued its own guidance.

The drugs safety body says weight-loss injections must not be taken:

• during pregnancy
• while trying to get pregnant
• during breastfeeding

Women should be told this information when they starting taking the jabs, but there are fears the message is not getting through.

Natasha Major, 26, started using Mounjaro to lose weight before planning to try for her third baby in a few years’ time, but was shocked six weeks later to find she was pregnant. She was taking the contraceptive pill at the time.

“I have polycystic ovaries as well, so I can’t get pregnant easily or quickly. So it was an even bigger shock that I had, which didn’t make any sense to me,” she says.

She then worried she could be harming the baby or it would not develop properly. Natasha rang her GP for advice and was told to stop taking it.

“We’re over the initial shock now and really happy, just wasn’t expected,” she says.

“The last injection I took, I found out about the pregnancy three hours later and haven’t taken it since then.

“I’ve had an early scan to make sure the pregnancy was viable and okay – baby had a little heartbeat and everything looks good,” Natasha says.

The MHRA, as well as doctors and pharmacists, are worried that popular GLP-1 medicines, known as Wegovy, Mounjaro, Saxenda, Victoza and Ozempic, are not being used safely.

These prescription medicines, which are licensed to treat obesity (and Ozempic for type 2 diabetes), make people feel full by mimicking a hormone released after eating. Mounjaro also acts on another hormone linked to appetite and blood sugar control.

They are only available on the NHS to people with a very high BMI, but can also be bought privately from high street and online chemists. Such is the demand for the jabs, they are also being sold illegally on social media and from beauty salons, without any medical advice or prescription, as a quick fix to lose weight.

The MHRA advises people to have a conversation with their prescriber about the risks and benefits of taking them, and understand the potential side-effects by talking to a doctor or pharmacist.

It has acted now because it has received around 40 reports relating to pregnancy made to its Yellow Card scheme, where the public can report suspected side-effects of medicines. Some of these have been unintended pregnancies.

Dr Alison Cave, chief safety officer at the MHRA, said there was evidence from animal studies “that these medicines may harm the unborn baby”.

“But we don’t know whether we have the same effects in humans, so much more data is needed to determine that.”

Women of child-bearing age are usually not included in clinical trials, which is why there is a lack of safety information for them.

“If you are taking this medicine and you are pregnant, you should talk to your doctor about stopping the medicine as soon as possible,” Dr Cave said.

Sukhi Basra, vice-chairwoman of the National Pharmacy Association, said women should visit their pharmacist for advice if they are confused about when to stop using the drugs, and always buy them from an official pharmacy.

Dr Bassel Wattar, pregnancy expert and consultant at Epsom and St Helier University Hospitals, said the implant or the intrauterine coil offered “more robust contraception” than the oral combined contraceptive pill while taking the injections.

Losing a lot of weight can sometimes help some women restore natural ovulation and boost their chances of becoming pregnant, but he said this should be planned under the care of specialist doctors “to ensure a pregnancy can be planned safely after a washout period off these drugs”.

BPAS, the British Pregnancy Advisory Service, says women in the UK “face significant challenges” when trying to access their contraceptive method of choice.

A lack of appointments, long waiting lists and high costs are just some of the barriers they face, BPAS said, as it called for a better plan for providing the choice women need.

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