Amphetamines are man-made stimulant drugs. Their effects usually last for several hours and include stimulation of the central nervous system, a sense of well-being and higher energy, a release of social inhibitions, and feelings of cleverness, competence and power. Effects are very much like an adrenalin rush, with breathing and heart rate increasing. The appetite is also suppressed, the body's temperature increases, the pupils become dilated, and there is an increased risk of dehydration. They have been used as medicines for instance for treating Attention-Deficit Hyperactivity Disorder (ADHD) or narcolepsy. They have also been used as performance-enhancing drug, for instance by athletes, pilots, and truck drivers. They have a bitter taste and usually come as a white, greyish white, pale pink or yellow powder, and sometimes as a brightly coloured tablet. Amphetamines can be snorted, swallowed, injected, dissolved in a drink or smoked.