Stimulants are the drugs which increase the activity on central nervous system so are called mood elevators or superman drugs. Use of stimulants can lead to insomnia, paranoia, brain damage, cardiac arrest, respiratory paralysis etc.
Stimulants, like cocaine and amphetamines, are highly addictive. These drugs mainly increase the activity of the CNS. Thus it can cause irregular heartbeat, feeling of exhilaration, anxiety, and even lead to heart attacks.
Some of Examples of stimulants are amphetamines, cocaine, nicotine, crack etc.