Amphetamines are powerful central nervous stimulants.
Most street speed contains amphetamine sulphate. Other amphetamines include dexamphetamine and methamphetamine, both less common and more powerful stimulants. Speed is usually sold as a white powder. Most people experience increased confidence, talkativeness and sociability, euphoria, increased energy, loss of appetite and insomnia. As the drug wears off and the person comes down from the effects, these feelings are replaced by a low matching the high given by the drug.