Epilepsy drugs may reduce effectiveness of hormonal contraceptives

People with epilepsy who use certain hormonal birth control methods may be at risk for reduced contraceptive effectiveness because of interactions with certain antiseizure medications, according to a study published October 7, 2026, in Neurology^®, the medical journal of the American Academy of Neurology. The study found that nearly one-third of people prescribed certain hormonal contraceptives were also prescribed antiseizure medications that can make those contraceptives less effective.

These findings are concerning because people with epilepsy can face additional health risks during pregnancy, and some antiseizure medications have been linked to risks for a developing baby. When pregnancy is not planned, effective contraception is especially important. Our study suggests many people may be prescribed combinations of medications that could reduce the effectiveness of some hormonal contraceptives and increase the risk of unintended pregnancy."

Laura Kirkpatrick, MD, study author, University of Pittsburgh School of Medicine and member of the American Academy of Neurology

Pregnancy planning can be especially important for people with epilepsy. Previous research has shown that people with epilepsy face increased risks of complications during pregnancy, and some antiseizure medications have been associated with risks to a developing baby. Unplanned pregnancy may also reduce opportunities to adjust medications and begin folic acid supplementation before pregnancy.

Researchers looked at medical records for 21,923 people with epilepsy who were prescribed hormonal contraceptives that can be affected by drug interactions and were also prescribed enzyme-inducing antiseizure medications.

The contraceptives included combined oral contraceptive pills, progestin-only pills, contraceptive patches, vaginal rings and subdermal implants. Researchers looked for overlap between those contraceptives and enzyme-inducing antiseizure medications, including carbamazepine, oxcarbazepine, phenobarbital, phenytoin, topiramate and several others.

A total of 7,154 people, or 32.6%, had at least one time of 14 days or longer when a contraceptive and an antiseizure medication overlapped. On average, the overlap lasted about seven months.

"It is important for people with epilepsy to know that not all forms of contraception are affected by these medication interactions," Kirkpatrick said. "With informed counseling, people can choose a contraceptive method that aligns with their preferences and health needs. Our study did not look at pregnancy outcomes or determine whether participants experienced contraceptive failure, so more research is needed to better understand the real-world impact of these overlapping prescriptions."

A limitation of the study was that prescription records do not show whether participants took medications as prescribed.

The study was supported by the National Institutes of Health.