During medical school, a neurologist taught me that the number one cause of headaches in the US was coffee.
That was news to me! But it made more sense when he clarified that he meant lack of coffee. His point was that for people who regularly drink coffee, missing an early morning cup, or even just having your first cup later than usual, can trigger a caffeine withdrawal headache. And considering how many daily coffee drinkers there are (an estimated 158 million in the US alone), it’s likely that coffee withdrawal is among the most common causes of headaches.