UK regulator warns Mounjaro and other GLP-1 drugs may weaken oral contraceptives

The UK's Medicines and Healthcare products Regulatory Agency (MHRA) issued its first public alert on contraception and weight-loss medicines on June 5, 2025, after receiving 40 reports relating to pregnancies in people using GLP-1 drugs including Mounjaro ^[1].

The agency said that Mounjaro, which contains tirzepatide, may reduce the effectiveness of oral contraceptives such as the pill in people who are overweight, and that women taking the medicine should use barrier contraceptives such as condoms ^[1]. The MHRA said it had received 26 pregnancy-related reports for Mounjaro ^[1].

It also reported eight reports relating to pregnancy in people taking semaglutide, the molecule in Ozempic, Wegovy and Rybelsus, and nine reports for liraglutide, which is found in another weight-loss drug, Saxenda ^[1]. Those three counts add up to 43, while the MHRA described a total of 40 reports; the difference is not explained in the article.

The MHRA said it is not necessary for women in the reports to say whether a pregnancy was unintentional, and that two of the reports said the pregnancy was unintended ^[1].

What the regulator told patients

The MHRA said these drugs must not be taken during pregnancy, while trying to get pregnant or while breastfeeding, because there is "not enough safety data to know whether taking the medicine could cause harm to the baby" ^[1]. In some instances, it said, women should keep using contraception for up to two months between stopping the medicine and trying to get pregnant ^[1].

Dr Channa Jayasena, a consultant in reproductive endocrinology and andrology at Imperial College Healthcare NHS Trust, said the reproductive effects may run in two directions at once. "Obesity reduces fertility in women. So, women with obesity taking GLP-1 drugs are more likely to get pregnant than before they lost weight," he said, adding: "In addition, we think that the absorption of oral contraceptive pills may be reduced with GLP-1 drugs which slow down emptying of the stomach, though more research is needed to confirm this" ^[1].

Dr Alison Cave, the MHRA's chief safety officer, said the medicines "are not a quick fix to lose weight and have not been assessed to be safe when used in this way" ^[1].

Why it matters for patients

The alert comes from a UK regulator, and it is not known whether the US Food and Drug Administration has issued comparable guidance or asked for a label change; that has not been reported. People in the United States who take Mounjaro, Ozempic, Wegovy or another GLP-1 and rely on a daily pill for birth control are therefore reading a warning that, so far, has been issued on the other side of the Atlantic.

The practical issue described is absorption. If a medicine slows the stomach emptying, an oral contraceptive may not be taken up the way it normally is, and the MHRA's advice to add a barrier method reflects that concern ^[1]. Jayasena said more research is needed to confirm the effect ^[1].

The second issue is what happens if a pregnancy does occur. The MHRA says there is not enough safety data to know whether these medicines could harm a baby, and it advises against taking them during pregnancy or while breastfeeding ^[1]. Jayasena noted that other forms of weight loss, such as weight-loss surgery, can increase the chance of miscarriage, while adding that how harmful GLP-1 drugs are during pregnancy is unknown ^[1].

The reports themselves do not establish that the drugs caused any pregnancy or any harm; they are accounts of pregnancies that occurred in people using the medicines ^[1].

What happens next

The MHRA guidance stood as of June 5, 2025, and no date for a further review has been disclosed ^[1]. Whether other regulators, including the FDA, take similar action has not been reported, and no timeline for any such step has been announced ^[1].