Antiseizure Medications Birth Control: What This Review Found

What was studied

Researchers systematically reviewed 17 clinical studies reported in 16 publications. The studies included 399 individuals and examined 15 antiseizure medications. Each study assessed how at least 5 days of an antiseizure medication changed exposure to the estrogen and progestin in a combined oral contraceptive.

The researchers used a network meta-analysis to compare medications indirectly. All contraceptives studied contained at least 30 micrograms of ethinylestradiol and either levonorgestrel or norethindrone, the two progestins considered least sensitive to enzyme induction.

What they found

Some antiseizure medications reduced exposure to contraceptive hormones, including medications often described as weak enzyme inducers. Brivaracetam at 100 mg/day reduced ethinylestradiol exposure more than levetiracetam at 1,000 mg/day. Lamotrigine at 300 mg/day had a greater effect on ethinylestradiol and levonorgestrel exposure than lacosamide at 400 mg/day.

In this analysis, topiramate at 50 mg/day and 200 mg/day had comparable effects on ethinylestradiol and norethindrone. The low dose also did not differ from weak enzyme inducers in its effect on ethinylestradiol exposure. The authors concluded that current recommendations may underestimate some interactions, particularly for newer combined oral contraceptives.

Limits of the evidence

This analysis measured hormone exposure rather than ovulation, pregnancy, or contraceptive failure, so it does not establish how the observed changes affect real-world pregnancy risk. Comparisons between medications were indirect rather than based on trials directly comparing every drug.

The evidence came from 399 individuals. Nine antiseizure medications were tested at doses 13% to 75% below their recommended maximum, leaving uncertainty about effects at higher doses. The contraceptives studied used at least 30 micrograms of ethinylestradiol and only the two progestins least vulnerable to induction, so the findings may not apply to lower-dose pills or pills containing other progestins. The abstract does not report the individual risk-of-bias findings.

For families and caregivers

The findings suggest that even some antiseizure medications considered weak inducers, including low-dose topiramate, may reduce exposure to hormones in combined birth control pills. However, lower hormone exposure does not necessarily mean that contraception will fail.

People with epilepsy and their families can discuss the specific antiseizure medication, dose, and contraceptive formulation with a clinician. For people taking weak inducers without an additional contraceptive method, the authors suggest that pills containing levonorgestrel or norethindrone might be preferable because these progestins appear less vulnerable to enzyme induction.

What to watch next

Larger, direct studies of newer and lower-dose contraceptives that also assess ovulation, pregnancy, or contraceptive failure would help clarify the clinical importance of these hormone-exposure changes.

Terms in this summary

Combined oral contraceptive (COC)

A birth control pill containing both an estrogen and a progestin.

Antiseizure medication (ASM)

A medicine used to prevent or reduce seizures.

Enzyme inducer

A drug that increases the activity of enzymes that break down other medicines or hormones, potentially lowering their levels in the body.

Cytochrome P450 3A4

A liver and intestinal enzyme that helps break down many medicines and hormones.

Exposure

The amount of a medicine or hormone present in the body over time.

Area under the concentration-time curve (AUC)

A measure of total drug or hormone exposure in the blood over a set period.

Network meta-analysis

A method that combines studies to compare several treatments, including some that were not tested directly against each other.

Progestin

A laboratory-made hormone with effects similar to progesterone that is used in many contraceptives.