Caffeine, a demonstrated cause of headache used by nearly everybody, may be the sole cause of the mysterious primary headaches that plague humankind, including the commonplace headaches called tension-type headache and the more severe headaches called migraine.

It may seem difficult to believe the cause of migraine and other primary headaches could have gone unrecognized despite being literally right under our noses. Yet caffeine possesses all the qualities needed to cause the entire phenomenon of primary headache. Caffeine withdrawal symptoms often include severe headache and nausea/vomiting, so caffeine withdrawal could explain the severe headache and nausea/vomiting typical of migraine. Caffeine use is highly prevalent enough to account for the high prevalence of primary headache. Caffeine withdrawal headaches, like primary headaches, are episodic. And caffeine's ability to relieve caffeine withdrawal headaches seems to readily explain caffeine's ability to relieve primary headaches.

Caffeine also seems able to account for many other aspects of primary headache, including the associations between migraine and female gender, mornings, weekends, sleeping in late, insomnia, alcohol, smoking, weather, overuse of headache medicines, stress, anxiety/panic disorder, depression, asthma, and epilepsy.

Medical science currently assumes primary headache can occur absent caffeine. According to the prevailing view among headache researchers and theorists, primary headaches are never caffeine withdrawal headaches, an assumption that has been integrated into the diagnostic criteria for migraine. Astoundingly, however, medical science hasn’t ruled out the possibility that caffeine causes all primary headaches. Certainly many migraine patients report using no caffeine, but such testimony has never been verified by objective testing. Primary headache has never been demonstrated to occur absent caffeine use; there’s no demonstrated example of primary headache occurring in a patient who doesn’t use caffeine. To put it yet another way: caffeine abstinence has never been verified in a primary headache patient.

The lack of a verified example of primary headache absent caffeine has a profound logical implication. It means it may be every migraine patient who reports caffeine abstinence is mistaken. It means it may be migraine cannot occur absent caffeine use. It means the prevailing assumption that primary headaches are never caffeine withdrawal headaches may be wrong, and the opposite true: it may be primary headaches are always caffeine withdrawal headaches. It may be migraine and caffeine withdrawal headache are one and the same condition, with one and the same cause. It may be caffeine causes all primary headaches.

Once alerted to this gaping hole in the prevailing view, headache researchers should have scrambled to fill it. Unfortunately, they are comfortable with their assumptions and feel no need to back them up with demonstrated evidence. I've listed the counterarguments I've encountered so far, along with my defenses, in a later section. That a lay author can so easily demolish the reasoning of top headache scientists shows how weak the prevailing view is.

Headache researchers consider the idea that caffeine might cause some or all migraine a kooky theory that doesn’t merit investigation. They are looking at it the wrong way. They need to support their own view with demonstrated evidence. To do that, they need to falsify the caffeine theory. The only way to eliminate the possibility that primary headache is always caffeine withdrawal headache, and—the other side of the same coin—the only way to substantiate the prevailing assumption that primary headache is never caffeine withdrawal headache, is to produce an example of primary headache occurring in a person whose caffeine abstinence has been verified by objective testing. So long as such an example is lacking, the prevailing view rests and depends on an undemonstrated assumption. The same trial study that would falsify the caffeine theory would simultaneously serve to falsify the prevailing view. Headache researchers may claim they aren’t obligated to investigate every unorthodox theory that comes out of left field, but they can’t justify their failure to test their own assumptions and the prevailing view that depends upon those assumptions.

Unable to effectively refute this argument, headache experts ignore it.

The working assumption in migraine research is that migraine is distinct and separate from caffeine withdrawal headache, yet researchers have never bothered to separate them. Researchers consistently neglect to rule out caffeine withdrawal headache during studies of migraine and migraine treatments. Because of this decided lack of scientific rigor, migraine headache and caffeine withdrawal headache, though supposed separate, remain confounded. The practical importance of this collective and ongoing scientific blunder depends on how much primary headache caffeine causes. Nobody knows what percentage of migraine is caffeine-caused; caffeine could cause zero percent of diagnosed cases of migraine, 100 percent, or any percentage in-between. The correct figure is likely greater than zero, as severe caffeine withdrawal closely resembles migraine, so must sometimes be diagnosed as migraine. It’s not known whether such diagnoses are never, sometimes, or always correct; it’s possible severe caffeine withdrawal headache not only resembles migraine, but sometimes or always is genuine migraine.

Fig 1, right: These Venn and Euler diagrams represent five possible logical relationships between primary headache and caffeine withdrawal headache. The circles marked PH contain all primary headache episodes that have ever occurred. The circles marked CWH contain all caffeine withdrawal headaches that have ever occurred.

Regardless of what the correct figure turns out to be, the possibility that caffeine causes some or all migraine is intriguing and promising. Because caffeine withdrawal headache closely resembles migraine, and the causal mechanism of caffeine withdrawal headache is known, caffeine withdrawal headache offers insight into the causal mechanism of migraine. Moreover, investigation may reveal that some or all patients with migraine, tension-type headache, chronic daily headache, cluster headache, and other primary headaches can eliminate their headaches by eliminating caffeine intake. The stakes are high. Primary headache including migraine isn't fatal or permanently disabling, but is painful and highly prevalent, so causes a vast amount of human suffering. Caffeine abstinence may prove a safe, effective, and cost-free treatment. For the sake of scientific rigor, and because of potential practical importance to the treatment of headache, it makes sense to investigate the relationship between caffeine and migraine.