Dopamine
Drug addiction and psychostimulants

The effects of psychostimulants include increases in heart rate, body temperature, and sweating; improvements in alertness, attention, and endurance; increases in pleasure produced by rewarding events; but at higher doses agitation, anxiety, or even loss of contact with reality. Drugs in this group can have a high addiction potential, due to their activating effects on the dopamine-mediated reward system in the brain. However some can also be useful, at lower doses, for treating attention deficit hyperactivity disorder (ADHD) and narcolepsy. An important differentiating factor is the onset and duration of action. Cocaine can take effect in seconds if it is injected or inhaled in free base form; the effects last from 5 to 90 minutes. This rapid and brief action makes its effects easily perceived and consequently gives it high addiction potential. Methylphenidate taken in pill form, in contrast, can take two hours to reach peak levels in the bloodstream, and depending on formulation the effects can last for up to 12 hours. These longer acting formulations have the benefit of reducing the potential for abuse, and improving adherence for treatment by using more convenient dosage regimens.
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