Catamenial Epilepsy
When seizure patterns appear to follow the menstrual cycle
Some people with epilepsy notice that their seizures repeatedly become more frequent at particular stages of the menstrual cycle.
When that increase follows a recurring menstrual pattern, it may be described as catamenial epilepsy.
Catamenial epilepsy is not a separate epilepsy syndrome. A person may have focal epilepsy, generalised epilepsy or another recognised epilepsy syndrome and also experience a menstrual-related increase in seizures.
The relationship between menstruation and seizures is biologically plausible because reproductive hormones interact with brain activity. However, the science is more complicated than simply saying that periods cause seizures.
What does “catamenial” mean?
The word catamenial refers to menstruation.
In epilepsy, it is used when seizure frequency appears to increase repeatedly during particular menstrual-cycle phases.
Epilepsy Action describes catamenial epilepsy as a pattern in which seizures worsen at certain times of the menstrual cycle. It can occur in both focal and generalised epilepsies.
A single seizure cluster during one period does not establish catamenial epilepsy.
The important feature is recurrence of the pattern over time.
Why might hormones affect seizures?
The brain and reproductive hormone systems communicate with each other.
Hormones such as oestrogen and progesterone can influence neuronal signalling and brain excitability.
Progesterone can be converted into neuroactive substances including allopregnanolone, which can enhance inhibitory GABA-related activity in the brain.
Falling progesterone levels have therefore been proposed as one reason seizure susceptibility may increase around menstruation in some people.
Oestrogen also affects neuronal activity, but describing it simply as a “seizure-causing hormone” would be inaccurate. Its effects vary according to hormone concentration, brain region, receptor activity and other biological factors.
The balance and timing of hormonal change may be more important than any single hormone acting alone.
The three traditional catamenial patterns
Research has traditionally described three main patterns: C1, C2 and C3.
These patterns were developed from studies comparing seizure frequency with different stages of the menstrual cycle.
C1 — Perimenstrual pattern
This is an increase in seizures around the start of menstruation.
It generally includes the days immediately before and after menstrual bleeding begins.
One proposed explanation is the rapid fall in progesterone that occurs before menstruation.
Because progesterone-derived neurosteroids can support inhibitory activity in the brain, their withdrawal may make seizures more likely in susceptible individuals.
C2 — Periovulatory pattern
This refers to an increase in seizures around ovulation.
Ovulation usually occurs during the middle portion of an ovulatory menstrual cycle, although the exact day varies between individuals and from cycle to cycle.
A rise in oestrogen before ovulation has been proposed as one possible mechanism, although the precise biological explanation remains uncertain.
C3 — Luteal-phase pattern
The third pattern occurs mainly in cycles where ovulation is absent or progesterone production during the luteal phase is inadequate.
Instead of a short rise in seizure frequency at one point, increased susceptibility may extend through a larger part of the second half of the cycle.
This is sometimes described as an inadequate luteal-phase pattern.
Are C1, C2 and C3 definite diagnoses?
They are useful research and clinical descriptions, but the science is evolving.
A major 2026 scoping review published in Epilepsia examined the way catamenial epilepsy has been defined across the scientific literature.
The researchers found substantial inconsistency.
More than half of the studies they reviewed did not clearly specify which diagnostic criteria they used, and many studies monitored seizures and menstrual cycles for only a short period.
The authors also highlighted another important problem: seizures can naturally occur in multiday or approximately monthly rhythms even in people who do not menstruate.
That means a seizure pattern occurring every few weeks is not automatically proof that menstruation is causing it.
This does not mean catamenial epilepsy is imaginary.
It means clinicians and researchers need to be more careful about distinguishing a true menstrual association from other naturally occurring seizure cycles.
How common is catamenial epilepsy?
Published estimates vary.
Some reviews and patient-information sources suggest that around 40% of women with epilepsy may experience some degree of menstrual-related seizure exacerbation.
However, the true figure is uncertain because studies have used different definitions, different diary periods and different thresholds for deciding what counts as catamenial epilepsy.
The 2026 review specifically warned that current diagnostic methods may over-attribute some monthly seizure rhythms to menstruation.
So prevalence figures should be regarded as estimates rather than exact numbers.
Does it occur only in focal epilepsy?
No.
Catamenial seizure patterns have been reported in both focal and generalised epilepsies.
The original research establishing the C1, C2 and C3 patterns included many people with focal seizures, but menstrual-related changes are not restricted to one epilepsy type.
Someone should therefore not be ruled out simply because they have a generalised epilepsy.
Can someone have catamenial epilepsy without ovulating?
Yes.
Menstrual bleeding does not always mean that ovulation has occurred.
Some cycles are anovulatory, meaning no egg is released.
Research has shown that menstrual-related seizure exacerbation can still occur during these cycles, particularly in patterns resembling the C3 inadequate-luteal-phase pattern.
How is catamenial epilepsy diagnosed?
There is no single scan, blood test or EEG that proves someone has catamenial epilepsy.
Diagnosis usually relies on identifying a repeated relationship between:
seizure frequency
menstrual-cycle timing
whether ovulation appears to occur
and the individual's usual seizure pattern.
Epilepsy Action advises keeping a seizure and menstrual diary for at least three months when investigating a possible pattern.
However, newer research suggests longer monitoring may sometimes be useful because seizure rhythms can occur over many months independently of menstruation.
What should be recorded?
A useful diary may include:
the first day of each period
how long bleeding lasts
seizure date and time
seizure type
seizure duration
seizure clusters
auras or warnings
sleep
illness
stress
missed or delayed medication
alcohol where relevant
medication changes
contraceptive changes
and recovery afterwards.
If periods are irregular, record that too.
The aim is not simply to record “seizure during period”.
The useful question is whether seizures repeatedly increase during a particular cycle phase compared with the person's own baseline.
What does the “two-fold increase” mean?
A commonly used research definition is approximately a two-fold increase in average daily seizure frequency during a vulnerable menstrual phase compared with other parts of the cycle.
This threshold came from influential research describing the C1, C2 and C3 patterns.
Epilepsy Action also refers to a possible diagnosis when seizures occur at roughly twice the usual frequency at similar cycle stages over several months.
But this is not a perfect diagnostic rule.
The 2026 review found that definitions across studies are fragmented, so the two-fold threshold should be viewed as a useful clinical and research guide rather than an absolute biological dividing line.
How is ovulation identified?
Sometimes the menstrual diary alone is enough to reveal a strong pattern.
In other cases, clinicians may consider:
menstrual-cycle dates
ovulation predictor kits
hormone measurements
basal body-temperature changes
or other reproductive-health information.
Epilepsy Action notes that hormone testing and ovulation kits may sometimes help specialists determine whether seizures correspond with particular cycle phases.
These methods are not necessary for everyone.
What if periods are irregular?
Irregular periods make catamenial patterns harder to interpret.
They may occur because of many factors including:
age
stress
weight changes
other medical conditions
reproductive disorders
epilepsy
or antiseizure medication.
If periods are very irregular, very infrequent or unusually heavy, it is worth discussing this separately with a GP or specialist rather than assuming it is simply part of epilepsy.
Does catamenial epilepsy mean the epilepsy is drug-resistant?
Not necessarily.
Someone can have a menstrual seizure pattern whether their epilepsy is otherwise well controlled or difficult to treat.
Some studies have found catamenial patterns among people with drug-resistant epilepsy, but catamenial epilepsy itself does not automatically mean that standard antiseizure medicines cannot work.
How is catamenial epilepsy treated?
There is no single universally effective treatment.
Management usually begins with making sure the person's underlying epilepsy treatment is appropriate.
A specialist may review:
seizure type
epilepsy syndrome
baseline seizure frequency
menstrual regularity
antiseizure medicines
contraception
reproductive plans
and whether there is a reproducible high-risk part of the cycle.
Treatment may then differ depending on whether cycles are regular or irregular.
Intermittent clobazam
Some specialists use clobazam for a limited number of days around the part of the cycle when seizures are most likely.
This approach is sometimes called intermittent or pulsed treatment.
Epilepsy Action lists clobazam as one medicine that may be prescribed during identified high-risk days.
Evidence exists from older clinical studies, but these studies were small and would not meet the standards expected of a large modern randomised trial.
Clobazam is also a benzodiazepine and can cause side effects such as drowsiness.
It should only be used according to an individual prescription.
Acetazolamide
Acetazolamide has also been used as an additional treatment in some people with catamenial epilepsy.
Evidence is limited.
One small retrospective study found that some participants reported a substantial reduction in seizures, but the sample was small and loss of effectiveness over time occurred in some people.
This means acetazolamide may be considered in selected cases, but it cannot be described as a proven treatment for everyone.
Progesterone treatment
Because falling progesterone has been linked biologically with some catamenial patterns, researchers have investigated progesterone treatment.
Results have been mixed.
A 2023 systematic review included 19 studies involving 457 participants.
Although case reports and uncontrolled studies sometimes suggested improvement, randomised controlled trials did not demonstrate clear effectiveness of progesterone or related treatments.
The Cochrane review reached a similarly cautious conclusion: the available evidence is too limited to establish a clearly effective hormonal treatment for catamenial epilepsy.
Therefore progesterone should not be regarded as a proven routine treatment.
Suppressing menstruation
For some people with severe, difficult-to-treat menstrual-related seizures, specialists may consider strategies that reduce or suppress menstrual cycling.
Research and clinical literature have described approaches involving:
medroxyprogesterone
gonadotrophin-releasing hormone analogues
and other hormonal strategies.
However, these treatments can affect:
fertility
bone health
bleeding patterns
mood
cardiovascular health
and other areas of health.
Evidence remains limited, and treatment must be individualised.
Why not just increase antiseizure medication each month?
Because changing antiseizure medication without medical supervision can be dangerous.
Taking extra medication may increase:
sedation
dizziness
falls
toxicity
medication interactions
and other side effects.
Reducing or stopping medication suddenly can also provoke seizures.
Any cyclical medication plan should be prescribed by an epilepsy specialist.
Contraception can complicate the picture
Hormonal contraception can alter normal menstrual bleeding and hormone patterns.
At the same time, some antiseizure medicines can reduce the effectiveness of certain contraceptives, while some hormonal contraceptives can change the blood level of particular antiseizure medicines.
For example, oestrogen-containing contraception can lower lamotrigine concentrations.
So when someone is being assessed for catamenial epilepsy, clinicians need to know:
which contraception is being used
when it was started
whether it has recently changed
and which antiseizure medicines are being taken.
Related Information Hub page:
Contraception and Epilepsy
Could other seizure triggers mimic a catamenial pattern?
Yes.
Periods can also coincide with:
poor sleep
pain
stress
anxiety
migraine
changes in appetite
dehydration
illness
and medication disruption.
Poor sleep and stress are commonly reported seizure triggers.
If these repeatedly occur around menstruation, they can contribute to an apparent cycle-related increase.
That does not rule out a hormonal contribution, but it demonstrates why careful recording is important.
The 2026 research changes how we should think about diagnosis
One of the most important recent developments is the recognition that epilepsy itself can have multiday rhythms.
Seizures do not always occur randomly.
Some people experience repeating cycles lasting days, weeks or around a month.
The 2026 Epilepsia review found that approximately monthly seizure cycles have also been identified in men, women and children.
Because of this, researchers warned that simply observing a roughly monthly seizure pattern may sometimes lead to menstrual attribution when another seizure rhythm is actually responsible.
This is an important distinction.
The question should not simply be:
“Do seizures happen every month?”
It should be:
“Does seizure risk consistently correspond with a specific menstrual phase more strongly than would be expected from the person's underlying seizure rhythm?”
That is one reason longer-term tracking may become increasingly important in future research.
Does this mean earlier catamenial research was wrong?
No.
There is strong biological evidence that reproductive hormones can influence neuronal excitability, and repeated menstrual-associated seizure patterns have been observed in many studies.
The newer research does not erase that.
Instead, it suggests that catamenial epilepsy needs more precise diagnostic criteria so genuine menstrual sensitivity can be separated from other seizure rhythms.
Science becoming more precise is not the same as science proving the phenomenon does not exist.
When should someone speak to their epilepsy team?
It is worth discussing a possible catamenial pattern if:
seizures repeatedly increase around menstruation
seizures repeatedly increase around ovulation
clusters occur at approximately the same cycle phase
previously controlled seizures return in a repeating menstrual pattern
seizure severity changes predictably across the cycle
periods become irregular
hormonal contraception appears to change seizure control
or menstrual symptoms make epilepsy harder to manage.
Taking a diary to the appointment can make the discussion much more useful.
What questions could you ask?
Useful questions might include:
Do my seizure records suggest a menstrual pattern?
How long should I continue tracking?
Could my seizure rhythm be unrelated to menstruation?
Could my medication affect my periods?
Could contraception affect my medication?
Is there evidence for intermittent treatment in my case?
Would hormone or ovulation testing add anything?
Should I see a gynaecologist as well as my epilepsy specialist?
The most important message
Catamenial epilepsy describes a repeating increase in seizures associated with particular menstrual-cycle phases.
The relationship is biologically credible, but diagnosis is not always straightforward.
C1, C2 and C3 remain useful patterns, yet newer research shows that seizures can also follow approximately monthly rhythms unrelated to menstruation.
That means good assessment requires more than noticing that seizures “seem monthly”.
Record the pattern carefully, compare seizures with menstrual-cycle timing, consider other triggers and take the information to an epilepsy specialist.
Treatment may involve adjustments to ordinary epilepsy care or, in selected people, additional cyclical treatment.
The evidence for specific hormonal therapies remains limited, and medication should never be changed without specialist advice.
Sources and further reading
Wong V, Nurse ES, Reynolds A, Cook MJ, Karoly PJ. Monthly or menstrual? A scoping review of catamenial epilepsy and non-menstrual seizure rhythms. Epilepsia. 2026.
This recent review examined 70 catamenial-epilepsy studies and highlighted major inconsistencies in diagnostic criteria and the difficulty of distinguishing menstrual patterns from other multiday seizure cycles.
Epilepsy Action — Periods and catamenial epilepsy.
UK information covering menstrual seizure patterns, diagnosis, tracking and treatment. Last modified November 2025.
Maguire MJ, Nevitt SJ. Treatments for seizures in catamenial epilepsy. Cochrane Database of Systematic Reviews. 2021.
Systematic review of hormonal and non-hormonal treatments and the limitations of the available evidence.
Nucera B, et al. Progesterone and its derivatives for the treatment of catamenial epilepsy: A systematic review. Seizure. 2023.
Review of 19 studies involving 457 participants; controlled trials did not establish clear effectiveness for progesterone treatment.
Herzog AG, et al. Three patterns of catamenial epilepsy. Epilepsia. 1998.
Influential study describing the C1, C2 and C3 patterns and proposing a two-fold increase in seizure frequency as a practical threshold.
Female sex steroids and epilepsy: reciprocal changes in reproductive systems, cycles and seizures. Epilepsia. 2023.
Review of interactions between reproductive hormones, epilepsy and menstrual health.
Information reviewed: September 2026.
This page provides general educational information and does not replace individual advice from an epilepsy specialist, GP, pharmacist, gynaecologist or other healthcare professional.
