Women taking weight-loss jabs such as Wegovy, Mounjaro, and Zepbound have been warned that their oral contraceptive pill may be less effective. Dr Wiljon Beltre, a board-certified bariatric and metabolic surgeon specialising in obesity management, advises using backup methods like condoms.
How GLP-1 medications affect birth control
The impact depends on the type of GLP-1. Dr Beltre explains that Wegovy itself does not directly block the pill but side effects like nausea and vomiting can prevent absorption. "If you take your daily pill and then throw up two hours later due to nausea, your body wouldn't have absorbed it yet. It's the same thing as missing a pill," he says. Severe diarrhoea can also flush hormones out before they work.
The same issue applies to Saxenda and Victoza.
Fast weight loss and fertility boost
Dr Beltre notes that extreme weight loss of 15 to 20% can reset hormones. "Women with PCOS or severe obesity who thought they were infertile can suddenly start ovulating again, giving a massive boost in natural fertility." Combined with ineffective contraception, this creates a "perfect storm for an unplanned pregnancy."
Mounjaro poses greater absorption issues
"Mounjaro can pose a direct absorption issue for birth control pills," Dr Beltre warns. It targets two gut hormones instead of one, slowing stomach emptying more significantly, especially when starting or increasing the dose. This can reduce peak contraceptive hormone absorption by around 20%, meaning the pill does not provide full protection.
Dr Beltre recommends using condoms for four full weeks after the first jab and for four full weeks after every dose increase if relying on oral birth control.
Alternative contraception options
For those experiencing frequent nausea from weight-loss jabs, Dr Beltre suggests switching to an IUS (intrauterine system), patch, or implant.
