Stimulants are drugs that make you feel more alert. Caffeine, found in tea, coffee and chocolate, is one example. Many plants contain naturally occurring stimulants (probably to deter invading insects) that in humans make the brain and body more active. Many stimulants, such as nicotine and cocaine, are harmful and addictive. Amphetamine, which was first made a century ago, is another well-known stimulant.