UK warns weight-loss drug users to use contraception after 40 unexpected pregnancies

In May, Britain's medicines regulator issued its first formal warning about an unexpected consequence of weight-loss drugs: they were making women pregnant. The Medicines and Healthcare products Regulatory Agency had logged forty cases of unintended pregnancies among users of medications like Ozempic, Wegovy, and Mounjaro—drugs that have become ubiquitous in recent years, prescribed and purchased by millions seeking to shed pounds.

The mechanism is straightforward enough. These medications work by mimicking a natural gut hormone called GLP-1, which tells the brain the stomach is full. They slow digestion, boost insulin production, and suppress appetite. The weight loss that follows can be dramatic. But there's a biological consequence that caught many users off guard: as the pounds came off, fertility returned. For women living with obesity, excess weight had dampened their reproductive capacity. Remove the weight, and that capacity rebounds. The drugs were inadvertently restoring the very thing many users weren't planning for.

Among the forty reported pregnancies, eight involved semaglutide (the active ingredient in Ozempic and Wegovy) and nine involved liraglutide (found in Saxenda). Two cases were explicitly flagged as unintended. The actual number of pregnancies may be higher; these are only the cases formally reported to regulators. Dr. Channa Jayasena, a reproductive endocrinologist at Imperial College Healthcare NHS Trust, explained the paradox plainly: obesity reduces fertility. Women taking these drugs are therefore more likely to conceive than they were before losing weight—a shift many hadn't anticipated or prepared for.

There's a second complication. The medications may interfere with how the body absorbs oral contraceptives. Because these drugs slow stomach emptying, birth control pills may not be absorbed as effectively, leaving women who believe they're protected actually vulnerable. The research on this interaction remains incomplete, but the risk is real enough that regulators felt compelled to act.

The MHRA's guidance is now explicit: these medications should not be used during pregnancy, while attempting to conceive, or while breastfeeding. The agency lacks sufficient safety data on fetal exposure. In some cases, women are advised to continue contraception for up to two months after stopping the medication before trying to get pregnant. Dr. Alison Cave, the MHRA's chief safety officer, also took the opportunity to push back against what she called the casual use of these drugs as cosmetic treatments. "Skinny jabs are medicines licensed to treat specific medical conditions," she said, "and should not be used as aesthetic or cosmetic treatments." They are not quick fixes, and they have not been tested as such.

The longer-term risks remain murky. Similar weight-loss interventions—bariatric surgery, for instance—have been associated with higher miscarriage rates. Dr. Jayasena noted that while the full picture of GLP-1 drugs in pregnancy is still emerging, the precautionary principle suggests women should do everything possible to prevent pregnancy while taking them. The regulatory alert is a first step: making visible a problem that had been invisible, and giving women and their doctors the information they need to make informed choices. What happens next depends on whether users actually receive and act on this guidance—and whether the drugs' manufacturers and prescribers take seriously the responsibility to ensure it reaches the people who need it most.