But what is unique about caffeine is the targeted way in which it interferes with one of the most important of all biological functions: sleep. Walker, in his 2017 book Why We Sleep, argues that the consumption of caffeine—the most widely used psychoactive stimulant in the world—“represents one of the longest and largest unsupervised drug studies ever conducted on the human race.” We now know the results of that study and, if Walker is to be believed, they are alarming.
