It goes on to specify that “Mounjaro may reduce the effectiveness of oral contraceptives in those 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. This only applies to those taking Mounjaro and is especially important for the four weeks after starting Mounjaro and after any dose increase.”
“If you take birth control pills by mouth, talk to your healthcare provider before you use Mounjaro. Birth control pills may not work as well while using Mounjaro. Your healthcare provider may recommend another type of birth control for 4 weeks after you start Mounjaro and for 4 weeks after each increase in your dose of Mounjaro.”
The MHRA warning calls out Mounjaro, specifically, regarding the possible disruption of birth control, but then goes on to remind women that none of the drugs should be taken during pregnancy, as the effects on a fetus are unknown.
“These medicines must not be taken during pregnancy, while trying to get pregnant, or during breastfeeding,” reads the warning. “Anyone who gets pregnant while using them should speak to their healthcare professional and stop the medicine as soon as possible. This is because there is not enough safety data to know whether taking the medicine could cause harm to the baby.”
Narula explained theories that the decreased effectiveness of birth control while taking any of these drugs is due to two factors: One, the fact that being obese or overweight, or having syndromes like PCOS can decrease your fertility, and that, with these drugs inducing weight loss, “you’re essentially changing your menstrual cycle, your ovulation, and increasing your chances of getting pregnant.”
The second issue, she explains, is that oral contraceptives work by getting absorbed into our body—but that GLP-1s work “by changing our gut motility,” which is how food and waste moves through the body, and can also sometimes cause nausea, vomiting, and diarrhea. “So you can put those two together and see how the GLP drugs changing your gut motility and potentially affecting absorption of oral contraceptive pills could cause you to also see an increase in fertility,” Narula said.
Regarding the other part of the warning, that the drugs should not be taken during pregnancy and should be stopped two months before attempting to conceive, she said, “We don’t study pregnant women in trials, it’s not considered safe. But what we do know from animal studies is that there can be some birth defects, growth restriction, even miscarriage.”
More on GLP-1 drugs:
