• Other drugs, such as cocaine or methamphetamine, can cause the nerve cells to release
abnormally large amounts of natural neurotransmitters (mainly dopamine) or to prevent
the normal recycling of these brain chemicals, which is needed to shut off the signaling
between neurons. The result is a brain awash in dopamine, a neurotransmitter present in
brain regions that control movement, emotion, motivation, and feelings of pleasure.
•As a person continues to abuse drugs, the brain adapts to the overwhelming surges in
dopamine by producing less dopamine or by reducing the number of dopamine receptors
in the reward circuit
• This decrease compels the addicted person to keep abusing drugs in an attempt to bring
the dopamine function back to normal, but now larger amounts of the drug are required to
achieve the same dopamine high—an effect known as tolerance
Doctors make a diagnosis of addiction if three or more of the following features are present:
• A strong desire or sense of compulsion to take the substance.
• Difficulties controlling the substance-taking behavior in terms of when it occurs,
consumed once started.
• A physically unpleasant withdrawal state when not consuming the substance.
Further substance use to relieve or avoid the withdrawal state.
•Evidence of increased tolerance (increased doses are required in order to achieve