Caffeine

Caffeine is a stimulant of the central nervous system belonging to a chemical family called methylxanthines. It occurs naturally in plants including coffee and tea and can also be added to products. Its familiar effect is to reduce drowsiness and increase wakefulness .¹

Caffeine crosses into the brain and blocks receptors for adenosine, a chemical involved in communication between cells. This receptor-blocking action is central to caffeine’s stimulant effects. Adenosine receptors also occur elsewhere in the body, so caffeine’s actions are not confined to alertness .¹

After absorption, caffeine is broken down mainly in the liver by an enzyme called CYP1A2. The resulting compounds include paraxanthine, theobromine, and theophylline, which are subsequently processed further and excreted. How quickly caffeine is cleared varies with physiological factors and some medicines, so its duration of action is not identical for everyone .¹

The response also depends on the amount consumed and individual sensitivity. Increased wakefulness is therefore only one part of caffeine’s effects; restlessness and difficulty sleeping can occur as well .¹