LONDON, United Kingdom (AFP) — The United Kingdom’s (UK) medicine regulator warned Thursday against taking “skinny jabs” to fight weight loss if trying to get pregnant or while breastfeeding because of their unknown effects on babies.

The Medicines and Healthcare products Regulatory Agency (MHRA) said popular jabs like Ozempic and Wegovy “must not be taken during pregnancy, while trying to get pregnant, or during breastfeeding”.

It urged women to use “effective contraception while taking these medicines and, in some cases, for up to two months between stopping the medicine and trying to get pregnant”.

“Anyone who gets pregnant while using them should speak to their healthcare professional and stop the medicine as soon as possible… because there is not enough safety data to know whether taking the medicine could cause harm to the baby,” it added.

Rebecca Reynolds, a professor of metabolic medicine at the University of Edinburgh, said there was “hardly any available data from human studies” to know if the weight loss drugs were safe in pregnancy.

“The data from animal studies suggests the potential for harm with low birthweight and skeletal abnormalities, though more evidence is needed to assess if there are risks of taking these drugs in humans,” she added.

The MHRA also warned about the impact of another weight-loss and diabetes injection, Mounjaro, on the effectiveness of oral contraception for people who are overweight.

“Therefore, those taking Mounjaro who are overweight and are using an oral form of contraception are advised to also use a non-oral form of contraception,” it said.

Ying Cheong, a consultant in reproductive medicine at the University of Southampton, called the MHRA’s advice “both timely and necessary”.

“Gastrointestinal side-effects such as vomiting and diarrhoea can impair oral contraceptive absorption, increasing the risk of unintended pregnancy,” he said.