Hormonal birth control introduces synthetic hormones, such as estrogen and progestin, to prevent pregnancy. Seizures are characterized by a sudden, uncontrolled burst of electrical activity in the brain that temporarily affects how a person moves or behaves. The relationship between birth control and seizures is a bidirectional interaction between reproductive hormones and the electrical stability of the brain. Contraceptive hormones can affect the brain’s seizure threshold, while certain anti-seizure medications can alter the effectiveness of the birth control itself. Understanding this interplay is important for individuals with pre-existing seizure disorders.
How Hormones Influence Seizure Threshold
The two primary female sex hormones, estrogen and progesterone, have opposing effects on neuronal excitability, which determines the brain’s seizure threshold.
Estrogen’s Proconvulsant Effect
Estrogen is proconvulsant, meaning it lowers the seizure threshold and increases the likelihood of a seizure event. This effect occurs because estrogen increases neuronal excitability, potentially by altering neurotransmitter functions.
Progestin’s Anticonvulsant Effect
Progesterone and its synthetic derivatives, progestins, are anticonvulsant and raise the seizure threshold. Progesterone achieves this protective effect primarily by modulating the Gamma-aminobutyric acid (GABA) receptor, the brain’s main inhibitory neurotransmitter system. By enhancing GABA activity, progesterone dampens the excessive electrical signaling that leads to a seizure.
The effect of combination birth control is a balance between the proconvulsant properties of synthetic estrogen and the anticonvulsant effects of the progestin component. The net effect on seizure frequency varies significantly between individuals, requiring careful monitoring.
Birth Control as a Management Tool for Seizures
Hormonal contraceptives are sometimes used therapeutically to manage Catamenial Epilepsy (CE), where seizures are triggered or made worse by natural fluctuations in the menstrual cycle. This condition is linked to the changing ratio of estrogen to progesterone throughout the month. Seizure frequency often peaks during the premenstrual and periovulatory phases, when the estrogen-to-progesterone ratio is higher.
The goal of using hormonal birth control is to suppress ovulation and maintain a stable, high level of progestin to counteract the natural hormone shifts. Continuous-use regimens, particularly those that are progestin-dominant, can be effective in reducing seizure frequency for individuals with CE. This stabilization eliminates the cyclical hormonal peaks and troughs, preventing the steep drop in progesterone that typically occurs just before menstruation.
Potential Interaction with Anti-Seizure Medications
The most significant practical concern for individuals with epilepsy using hormonal birth control is the drug-drug interaction with certain Anti-Seizure Medications (ASMs).
ASMs Reducing Contraceptive Efficacy
Many ASMs are classified as hepatic enzyme inducers, meaning they stimulate the production of enzymes in the liver, specifically the cytochrome P450 system. When taken concurrently, these enzyme-inducing ASMs (e.g., phenytoin, carbamazepine, and phenobarbital) accelerate the breakdown and metabolism of the synthetic estrogen and progestin. This accelerated metabolism reduces the concentration of contraceptive hormones to subtherapeutic levels, drastically lowering birth control efficacy. The primary risk is contraceptive failure, leading to an unplanned pregnancy, which is concerning due to the potential teratogenic effects of some ASMs on a developing fetus.
Contraceptives Affecting ASM Efficacy
The interaction can be bidirectional, as hormonal contraceptives containing estrogen can reduce the blood levels of certain ASMs, such as lamotrigine and valproate. This decrease in ASM concentration can lead to a loss of seizure control or an increase in seizure frequency. Conversely, non-enzyme-inducing ASMs, including levetiracetam and gabapentin, do not significantly affect the metabolism of hormonal contraceptives, making them safer options.
Evaluating Risk and Selecting Contraception
Selecting the right contraceptive method requires a thorough evaluation of the individual’s seizure disorder, the specific ASMs being used, and the desired level of pregnancy prevention. For individuals taking enzyme-inducing ASMs, contraceptive methods that bypass first-pass metabolism in the liver are preferred. Long-acting reversible contraceptives (LARCs) are recommended because their effectiveness is less dependent on systemic hormone levels and daily adherence.
Highly effective options that are not affected by enzyme-inducing ASMs include:
- The levonorgestrel-releasing intrauterine device (IUD), which minimizes systemic exposure.
- The copper IUD, which is completely non-hormonal.
- Injectable methods, such as depot medroxyprogesterone acetate (DMPA).
High-dose estrogen methods are discouraged due to estrogen’s proconvulsant properties and the high risk of interaction with ASMs. All decisions must be made in consultation with both a neurologist and a gynecologist to ensure seizure control and contraceptive efficacy are maintained.