What is Amphetamine & Its Effects — Know the Facts Amphetamine is a powerful stimulant that affects the central nervous system. It increases the activity of certain brain chemicals, especially dopamine and norepinephrine, which is why people may feel more alert, energetic, focused, or confident after taking it. In medical settings, closely related substances may be prescribed under strict supervision for specific conditions. Outside of that context, amphetamine is often misused for studying long