This is important, Dr. X. Henry Hu of Merck & Co., Inc., in West Point, Pennsylvania, and colleagues say, because early treatment with migraine drugs called triptans can help reduce headache severity. (Merck makes one of these drugs, Maxalt, and funded the study.)

Hu and his associates had roughly 1500 migraine sufferers complete a 10-minute survey, and asked them to complete a second survey after their next migraine. About 60 percent (877 people) filled out the follow-up survey. Nearly 80 percent of the participants in each group were women.

Only about 4 percent of those who filled out the second survey were able to predict the exact date of their next migraine.

About 20 percent were able to predict their next migraine within 3 days, while 47 percent were able to accurately predict time of day of their next migraine attack and about 70 percent were able to predict the location of their next attack.

While premenopausal women, who may suffer headaches around the time of their period, might have been expected to predict their next migraine more accurately, their predictions were no more accurate than others'. This may be because women will suffer migraines at other times as well, Hu and his team say.

In the past 3 months, the vast majority of migraine sufferers surveyed (about 93 percent) reported that they were forced to change daily plans because of migraine.

One in five said they had avoided a work-related commitment because they were afraid of getting a migraine, while 27 percent reported canceling a work commitment for this reason. Around 28 percent said they had avoided or canceled social commitments due to fear of migraines.

The unpredictability of migraines, Hu and his colleagues say, could contribute to people's anxiety and fear about them. Because of the lack of predictability of future migraine attacks, migraine sufferers may benefit from increased education on the importance of keeping medications available at all times, they conclude.