Catamenial epilepsy is a pattern of seizure worsening tied to specific phases of the menstrual cycle, affecting roughly a third to over 40 percent of women with epilepsy depending on how strictly it is defined.1PubMed. Catamenial epilepsy: definition, prevalence pathophysiology and treatment2PubMed Central. A Clinical Approach to Catamenial Epilepsy: A Review The word “catamenial” comes from the Greek for “monthly,” and the condition has been recognized in some form for centuries. What makes it both fascinating and frustrating is that it sits at the intersection of neurology and reproductive endocrinology, two fields that have not always talked to each other well enough.
Three Distinct Seizure Patterns
Not all catamenial seizures cluster at the same point in the cycle. Researchers have identified three patterns, usually labeled C1, C2, and C3, each tied to a different hormonal window.3PubMed Central. Treatments for seizures in catamenial (menstrual‐related) epilepsy The perimenstrual pattern (C1) is the most common: seizures cluster in the days just before and after the start of a period, roughly day minus three through day plus three. The periovulatory pattern (C2) involves increased seizures around midcycle, when ovulation occurs. The luteal pattern (C3) is seen in women who have anovulatory cycles, where progesterone stays low throughout the entire second half of the cycle, leaving a broad window of vulnerability from around day ten all the way to menstruation.4PubMed. Catamenial epilepsy: Update on prevalence, pathophysiology and treatment from the findings of the NIH Progesterone Treatment Trial
These patterns are not mutually exclusive. A woman can show more than one, and the patterns can shift over time as reproductive hormone levels change. What they share is a common thread: seizures tend to worsen when estrogen is relatively high compared to progesterone, or when progesterone drops sharply.
Why Hormones Affect Seizure Thresholds
The prevailing view among researchers is straightforward in principle: estrogen tends to excite the brain, while progesterone tends to calm it.5PubMed Central. The influence of gonadal hormones on neuronal excitability, seizures, and epilepsy in the female Estrogen ramps up the activity of excitatory signaling in the brain, boosting the response to glutamate, the brain’s main “go” signal. It also appears to physically alter brain structure at a microscopic level by increasing the density of tiny branch-like connections between nerve cells.6PubMed. Interactions between hormones and epilepsy The net effect is a brain that is more easily pushed toward seizure activity when estrogen is dominant.
Progesterone works the opposite way, but not directly. The key player is actually a metabolite of progesterone called allopregnanolone, a neurosteroid produced in the brain itself.7PubMed Central. Neurosteroids and Seizure Activity Allopregnanolone enhances the activity of GABA, the brain’s main “stop” signal. When allopregnanolone levels are high during the second half of a normal menstrual cycle, the brain has a stronger natural brake on runaway electrical activity. When those levels crash premenstrually, the brake loosens.
This crash is not just a matter of losing a calming influence. The brain adapts to the presence of allopregnanolone during the luteal phase, and when it suddenly disappears, a rebound effect occurs. Specifically, the sudden withdrawal triggers changes in the composition of GABA receptors themselves: a subunit called alpha-4 gets upregulated in the hippocampus, making those receptors less effective at inhibiting nerve firing.8PubMed Central. Neurosteroid withdrawal regulates GABA-A receptor α4-subunit expression and seizure susceptibility by activation of progesterone receptor-independent early growth response factor-3 pathway In animal studies, this withdrawal produced a threefold increase in alpha-4 expression and was accompanied by measurably higher seizure susceptibility and increased anxiety.9PubMed Central. Progesterone withdrawal increases the alpha4 subunit of the GABA(A) receptor in male rats in association with anxiety and altered pharmacology – a comparison with female rats So the perimenstrual seizure surge is not simply the absence of protection; it is an active destabilization of the brain’s inhibitory circuitry.
Diagnosing Catamenial Epilepsy
The biggest obstacle to recognizing catamenial epilepsy is that no one-time test can confirm it. The diagnosis depends on documenting a consistent relationship between seizure timing and menstrual cycle phase over at least two to three months. Women need to keep daily records of both seizure events and menstrual cycle days, then those logs are analyzed to see if seizure frequency statistically doubles or more during the vulnerable windows compared to other cycle phases.
This sounds simple, but in practice it is surprisingly hard. Many women with epilepsy do not have perfectly regular cycles, especially if they are taking certain anti-seizure medications that affect hormone metabolism. Anovulatory cycles, which are more common in this population, change which pattern is relevant. And the threshold for what counts as catamenial varies across studies, which is one reason prevalence estimates range from about a third to over 40 percent.10PubMed. Catamenial epilepsy: definition, prevalence pathophysiology and treatment11PubMed Central. The Frequency of Catamenial Epilepsy in Female Epileptic Patients of Reproductive Age Group Presented to the Tertiary Care Hospital One study at a tertiary care hospital found catamenial patterns in about 40 percent of female epilepsy patients of reproductive age, with EEG confirmation of increased seizure activity during specific cycle phases.
Smartphone apps designed for seizure and cycle tracking are being explored as tools to make diagnosis easier. A feasibility study of one such app, called Seizure Cycle, showed that the technology is usable and can flag potential catamenial patterns, though the study was small and the C3 pattern proved especially hard to classify clearly.12PubMed. Seizure Cycle app: A feasibility study The condition remains underdiagnosed partly because many neurologists do not routinely ask women to track their cycles alongside their seizures, and partly because the diagnostic method requires patience that clinical workflows do not always accommodate.
The Mixed Evidence on Progesterone Treatment
Given that falling progesterone appears to trigger seizures, supplementing progesterone during vulnerable phases seems like an obvious fix. The reality has proved more complicated. The largest and most rigorous test of this idea was an NIH-funded randomized trial that compared cyclic natural progesterone to placebo in women with drug-resistant partial epilepsy. The headline result was disappointing: overall, progesterone was not significantly better than placebo at reducing seizure frequency.13PubMed Central. Progesterone vs placebo therapy for women with epilepsy: A randomized clinical trial
But the secondary analysis told a more nuanced story. Among the roughly one in five women whose seizures were most strongly concentrated in the perimenstrual window (with a high “C1 level”), progesterone showed clear separation from placebo. In that subgroup, about 38 percent responded to progesterone compared to 11 percent on placebo, and seizure frequency reductions ranged up to 71 percent for progesterone versus 26 percent for placebo as the degree of perimenstrual clustering increased.14PubMed Central. Progesterone vs placebo therapy for women with epilepsy: A randomized clinical trial A separate smaller study of women with intractable catamenial epilepsy found that adding progesterone tablets during the second half of the cycle significantly reduced seizure counts compared to placebo.15PubMed Central. Progesterone therapy in women with intractable catamenial epilepsy
A systematic review of progesterone and its derivatives for catamenial epilepsy concluded that the anti-seizure effect is likely mediated through allopregnanolone rather than progesterone itself, which may explain why some trials succeed and others do not: the amount of progesterone that actually gets converted to allopregnanolone varies between individuals.16PubMed. Progesterone and its derivatives for the treatment of catamenial epilepsy: A systematic review The takeaway for clinicians is that progesterone supplementation is worth considering for women with a strong perimenstrual pattern, but it is not a blanket solution for all catamenial epilepsy.
Other Treatment Strategies
Because progesterone does not work for everyone, several other approaches have been used, mostly involving cycling existing medications around vulnerable days rather than taking them continuously.
Intermittent clobazam, a benzodiazepine, has been studied for decades in this context. In a long-term follow-up study, women who took clobazam for about ten days around menstruation in each cycle achieved complete freedom from perimenstrual seizures in some cases, with several patients sustained for more than three years. The key finding was that tolerance to clobazam’s anti-seizure effect did not develop despite years of cyclical use, which distinguishes this approach from the daily benzodiazepine use that often loses effectiveness over time.17PubMed Central. Intermittent clobazam for catamenial epilepsy: tolerance avoided A few patients did experience rebound seizures between clobazam courses, so the strategy is not without trade-offs.
Acetazolamide, a carbonic anhydrase inhibitor originally developed for other conditions, is another option. In a study of women with catamenial epilepsy, 40 percent achieved at least a 50 percent reduction in seizure frequency. The drug worked equally well whether given continuously or intermittently, and the response was similar across different seizure types.18PubMed. Acetazolamide in women with catamenial epilepsy
Hormonal treatments that suppress the menstrual cycle entirely, inducing amenorrhea, have also been shown to reduce catamenial seizures. This makes biological sense: if the hormonal fluctuations driving the seizure pattern are eliminated, the pattern disappears. Continuous hormonal contraception or GnRH agonists can achieve this, though these approaches carry their own side effects and are not suitable for women who wish to become pregnant.19PubMed Central. A Clinical Approach to Catamenial Epilepsy: A Review
Anti-Seizure Drugs and Reproductive Hormones Can Interfere with Each Other
One of the most practically important and commonly overlooked aspects of catamenial epilepsy is the bidirectional relationship between anti-seizure medications and reproductive hormones. Certain older anti-seizure drugs, particularly those that rev up liver enzymes, speed the breakdown of steroid hormones. This means they can reduce the effectiveness of hormonal contraceptives, increasing the risk of unplanned pregnancy. The same enzyme-inducing drugs can also lower circulating progesterone levels, which could theoretically worsen the very hormonal imbalance driving catamenial seizures.20PubMed. Epilepsy, sex hormones and antiepileptic drugs in female patients
The interference runs in the other direction too. Anti-seizure medications can affect reproductive health directly through brain-level effects on the hormonal signaling centers, not just through liver metabolism.21PubMed. Epilepsy, sex hormones, and antiepileptic drugs Valproic acid, for example, has been linked to polycystic ovary syndrome and excess androgens in women with epilepsy, even though it inhibits rather than induces liver enzymes.22PubMed. Epilepsy, sex hormones and antiepileptic drugs in female patients Women with epilepsy already develop features of polycystic ovary syndrome at higher rates than expected, and certain medications may compound that risk.23PubMed Central. Polycystic ovaries and polycystic ovary syndrome in epilepsy: evidence for neurogonadal disease Since polycystic ovary syndrome is associated with anovulatory cycles, it could push women into the C3 catamenial pattern, creating a vicious cycle where the medication meant to control seizures inadvertently worsens a hormonal imbalance that triggers more seizures.
For these reasons, choosing and managing medications in women with catamenial epilepsy requires attention to both the seizure and reproductive dimensions simultaneously. That includes selecting contraceptive methods that are not undermined by enzyme-inducing drugs and monitoring for hormonal side effects of anti-seizure therapy.
How Catamenial Epilepsy Changes Across Life Stages
Catamenial epilepsy is by definition linked to the reproductive years, but it does not simply appear at puberty and vanish at menopause. The transitions between life stages bring their own complications. One study found that women with catamenial epilepsy had an average age of epilepsy onset around 17, compared to about 28 for women with epilepsy but without a catamenial pattern.24American Epilepsy Society. Catamenial Epilepsy; the Association of Age of Menarche in Women with Epilepsy Only about a third of the catamenial group had epilepsy onset before or during the year they started menstruating, suggesting that for many, it is the establishment of regular hormonal cycling rather than puberty itself that unmasks the pattern.
Perimenopause is often the worst period. In a study tracking seizure patterns across the menopausal transition, women with a history of catamenial seizures were significantly more likely to experience worsening during perimenopause, the years of erratic hormonal fluctuation before periods stop entirely.25PubMed. The effect of menopause and perimenopause on the course of epilepsy This makes sense physiologically: perimenopause involves wild, unpredictable swings in estrogen and progesterone, exactly the kind of instability that destabilizes seizure thresholds. But once menopause was established and hormone levels settled at their new low baseline, the same women were significantly more likely to see their seizures improve. The catch is that hormone replacement therapy during menopause could reintroduce the hormonal fluctuations and potentially re-trigger the pattern, though this has not been as rigorously studied.
Neurosteroid Drugs in the Pipeline
Because the mechanism of catamenial epilepsy centers on neurosteroid withdrawal and GABA receptor changes, researchers have been developing synthetic neurosteroids that could replace what the brain loses premenstrually without requiring the full hormonal cascade of progesterone supplementation. The most studied candidate is ganaxolone, a synthetic analog of allopregnanolone that targets the same GABA receptor sites but cannot be converted back into reproductive hormones, avoiding the systemic hormonal side effects of progesterone.
Animal models have been essential to this research. A rat model using pseudopregnancy and then neurosteroid withdrawal successfully mimicked the increased seizure susceptibility seen in perimenstrual catamenial epilepsy, giving researchers a reliable way to test new treatments.26PubMed. Neurosteroid withdrawal model of perimenstrual catamenial epilepsy A mouse model took this further, showing that neurosteroid withdrawal produced not just more frequent and more intense seizures but also reduced sensitivity to benzodiazepines and enhanced sensitivity to neurosteroids, closely mimicking what is seen clinically.27Journal of Pharmacology and Experimental Therapeutics. A Mouse Kindling Model of Perimenstrual Catamenial Epilepsy The reduced benzodiazepine sensitivity is worth noting because it helps explain why standard rescue medications may be less effective during catamenial flares.
In the rat model, ganaxolone showed enhanced anti-seizure potency specifically after neurosteroid withdrawal, meaning it worked better in the exact scenario it would be needed for clinically.28The Journal of Pharmacology and Experimental Therapeutics. Enhanced Anticonvulsant Activity of Ganaxolone after Neurosteroid Withdrawal in a Rat Model of Catamenial Epilepsy Ganaxolone has already received FDA approval for seizures associated with CDKL5 deficiency disorder, a rare genetic epilepsy, and investigations into its use for catamenial epilepsy are ongoing. The appeal is clear: rather than supplementing a reproductive hormone and hoping enough of it converts to the right neurosteroid, a synthetic neurosteroid could go directly to the receptor that matters.
The Brain’s Electrical Signature During the Cycle
Researchers have also been able to measure the cyclical changes in brain excitability directly. A study using transcranial magnetic stimulation, which delivers a brief magnetic pulse to the brain’s surface and measures the response, found that women with catamenial epilepsy had measurable changes in cortical excitability across their menstrual cycle. Specifically, a marker of the brain’s inhibitory capacity called the cortical silent period was significantly shorter during the luteal phase and menstruation compared to the follicular phase.29PubMed. Cyclical excitability of the motor cortex in patients with catamenial epilepsy: a transcranial magnetic stimulation study A shorter silent period means the brain’s inhibitory brakes are weaker during those phases, consistent with the hormonal mechanism described earlier. This kind of objective measurement could eventually supplement seizure diaries for diagnosis, though it remains a research tool for now.
The finding also has a subtler implication. It suggests that even on days when no seizure actually occurs, the brain of a woman with catamenial epilepsy may be operating with reduced safety margins during certain cycle phases. That reduced margin could make seizures more likely in response to triggers that would not ordinarily be a problem: missed sleep, stress, a skipped medication dose. Women who notice that their seizure triggers seem to be more potent at certain times of the month may be experiencing exactly this phenomenon, and naming it for what it is can be validating.
Contraception and Pregnancy Planning
The interaction between anti-seizure drugs and hormonal contraception deserves practical attention because the stakes are high. An unplanned pregnancy in a woman taking teratogenic anti-seizure medications carries risks that planned pregnancies, with medication adjustments made in advance, can largely avoid. Enzyme-inducing anti-seizure drugs reduce the blood levels of hormones in combined oral contraceptives, the patch, and the ring, potentially rendering them unreliable. Non-hormonal methods like copper IUDs, or hormonal IUDs that act locally rather than systemically, are generally unaffected and are often recommended as first-line options.
For women on progesterone supplementation specifically for catamenial epilepsy, the exogenous progesterone provides some contraceptive effect in its own right during the days it is taken, but the cyclical dosing used in most catamenial treatment protocols does not provide reliable contraception across the full cycle. Women should not assume that therapeutic progesterone doubles as birth control. The broader point is that contraception, seizure management, and hormonal treatment need to be coordinated as a single plan rather than managed piecemeal by different providers who may not be communicating with each other.