The 'detox' teas you see on Instagram can lead to unexpected pregnancies.

Diet teas could interfere with contraception and lead to an unexpected pregnancy, a leading gynaecologist has warned.

Dr Virginia Beckett, from the UK, told The Sun Online: “Detox teas which contain senna leaf may have a laxative affect which can cause diarrhoea or vomiting.

“If this happens, the effectiveness of the contraceptive pill may be reduced.”

The expert warns that if women have severe diarrhoea or vomiting, condoms should be used in addition to the Pill.

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“If a woman vomits within two hours of taking the contraceptive pill, it may not have been fully absorbed into her bloodstream so she should take another pill straight away,” she said.

The advice is to continue to take their pill as normal but use additional contraception while ill and for two days after recovering and if symptoms persist to see your doctor.

Australian Medical Association president, Dr Michael Gannon, also warned that women could get easily get “caught out”.

“As little as one or two missed pills can be enough for it to fail,” he told Mamamia.

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Dr Gannon said reducing transit times of medications in the gut may reduce their effectiveness – including the pill.

“You should always be very careful before you put something in your body… and when it comes to so-called detox it’s an absolute myth,” he said.

“The only form of detoxification is to drink plenty of water, sleep properly and eat healthily.”

Dr Gannon said long acting reversible contraception (LARC) could be a better option for women than the pill.

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“Unlike the pill, [LARC’s] are not prone to changes in gastrointestinal absorption that might come from vomiting or interactions with food stuffs or simple forgetfulness.,” said Dr Gannon.

The Better Health Channel warns that oral hormonal contraception is very effective in preventing pregnancy but only when used correctly.

“Oral hormonal contraception is more than 99 per cent effective in preventing pregnancy, when used the right way,”the website states.

“Given mistakes that can happen, such as missing a pill or running out of pills, it is only around 91 per cent effective.”

Brian Morton, from the Australian Medical Association Council of General Practice, says it is best to avoid buying the teas.

“Senna is going to cause diarrhoea and you’re going to lose a lot of fluid with it, so there’s a much higher risk of dehydration and also a loss of vitamins that our bodies really need,” he told ABC News.

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Brittany, a 19-year-old student from Melbourne, told ABC drinking a detox tea made her ill.

“At first, it did make me feel energised. But after doing it for a few days it made me pretty sick. I had really bad stomach cramps … and I couldn’t stop [going to the toilet],” she said.

A host of celebrities endorse diet teas that are said to contain senna leaf.

Singer Demi Lovato came under fire in April for promoting a 30-day detox with Teami tea products.

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“This year is all about #selflove,” Lovato said in an Instagram post.

Reality star Kylie Jenner and her sisters Kourtney and Khloe Kardashian also promote “natural” Flat Tummy Tea.