There is no clear dividing line between drug use and drug abuse. For that matter, there are no clear dividing lines between drug use, dependency on drugs, and drug addiction. There are many psychoactive drugs. Most of the time, these drugs also activate neural reactions, but at this level we have to be careful. For example, one stimulant administered directly to the reticular formation can awaken and arouse a sleeping cat, but if that same drug is administered to a different area of the reticular formation, the cat will go to sleep.
Caffeine is one of the most widely used stimulants.
It is an ingredient in many soft drinks, notably colas. In moderate amounts, it seems to have no life-threatening effects on the user. At some point, a mild dependence may develop. Caffeine disrupts sleep, making it more difficult to get to sleep in the first place and more difficult to stay asleep. After long or excessive use, giving up sources of caffeine may result in the pain of withdrawal.