Caffeine acts as a stimulant by displacing adenosine in the brain. Notice the similarity of the words “caffeine” and “adenosine.” Adenosine — you may recall from high school biology — is involved in ATP (adenosine triphosphate) and energy cycling in cells. However, the actions of caffeine are complex and not fully understood. A daily caffeine habit is probably the most common cause of worsening headaches. >> read more >>