Many women experience headaches caused by changes in their hormones.
These so-called "menstrual migraines" tend to be particularly severe.
"Migraine is most likely to develop in either the 2 days leading up to a period or the first 3 days during a period. This is because of the natural drop in oestrogen levels at these times.
"The attacks are typically more severe than migraines at other times of the month and are more likely to come back the next day," she says.
Periods are not the only trigger of hormone headaches.
Other causes include:
- the combined oral contraceptive pill – some women find their headaches improve while they're on the pill, but others report more frequent attacks, especially in the pill-free week, when oestrogen levels drop
- the menopause – headaches usually worsen as you approach the menopause, partly because periods come more often and partly because the normal hormone cycle is disrupted
- pregnancy – headaches can get worse in the first few weeks of pregnancy, but they usually improve or stop completely during the last 6 months; they do not harm the baby
It's worth keeping a diary for at least 3 menstrual cycles to help you check whether your migraines are linked to your periods.
If they're linked, a diary can help to pinpoint at what stage in your cycle you get a migraine.
The Migraine Trust has an online headache diary, which may be a useful tool.
If keeping a diary reveals that your headaches develop just before your period, you can try these tips to help prevent a migraine:
- Eat small, frequent snacks to keep your blood sugar level up. Missing meals or going too long without food can trigger attacks. Have a small snack before going to bed, and always eat breakfast. Here are 5 healthy breakfasts
- Have a regular sleep pattern, and avoid too much or too little sleep. Find out how to get a good night's sleep
- Avoid stress. If this proves difficult, find ways to deal with stress, such as taking regular exercise and using relaxation strategies. Use these 10 stress busters
Your doctor can also prescribe anti-migraine medicines for you to take around the time of your period.
These do not contain hormones, but they can help stop the headaches developing.
They include tablets called triptans and a type of painkiller called mefenamic acid.
Continuous contraceptive pills
Talk to your doctor if you think your contraceptive pills are making your migraines worse.
If you have headaches during the days you do not take the pills, you can avoid the sudden fall in oestrogen by taking several packs continuously without a break.
Hormone replacement therapy
The hormone changes that happen as women approach the menopause mean that all types of headache, including migraines, become more common.
But if you have migraines, it's best to use patches or a gel, as these types of HRT keep hormone levels more stable than tablets and are less likely to trigger migraines.
If you have regular periods, a doctor can prescribe an oestrogen gel or patch, which you use before your period is due and for a few days during your period.
But these are not commonly prescribed for menstrual migraines.