Is Caffeine a stimulant?

-Karthik Gurumurthy

Caffeine does not stimulate directly ; instead it blocks the action of another chemical, naturally present in the human body, that has a calming effect on the activity of cells, especially those in the brain and spinal cord.

Caffeine is present in coffee, tea and cocoa. If you study Organic Chemistry, you will learn all of them are part of  group of chemicals called methyl xanthines that temporarily occupy the same cell receptors as adenosine, a chemical produced by the body’s energy metabolism. Adenosine is a neuromodulator, a substance that normally acts as a brake on nerve cell activity by keeping cells from staying excited too long. When adenosine’s action is blocked by caffeine, nerve cells are more active.

Caffeine enters the brain very rapidly and stays active for several hours, but its effects drop off more quickly than those of some other stimulants. The time needed for caffeine concentrations in the bloodstream to drop by half is about three to six hours in a healthy adult, compared with about ten hours for methamphetamine.