Caffeine is a substance which is present primarily in coffee, but also in other foodstuffs, such as coca cola, tea and chocolate. It is perfectly legal, and many people fail to see it even as a danger to their health. However, it is as much a stimulant drug as any other, and, as such, can adversely affect your body. This is especially true if taking other drugs, whether legal or illegal, at the same time. NEVER GIVE PEOPLE BLACK COFFEE TO DRINK IN AN EMERGENCY SITUATION. IT MAKES THE DRUGS IN THEM WORK MORE QUICKLY.