Key ideas

• Psychoactive drugs affect behavior and mental processes.
• Psychoactive drugs can be classified based on the mechanism by which they affect neurotransmission, or by the effect they have on the person taking them.
• By mechanism, agonists mimic a neurotransmitter and activate its receptors, antagonists reduce its effect such as by blocking receptors, and reuptake inhibitors leave more neurotransmitter in the synapse.
• By effect, stimulants increase central nervous system activity, depressants decrease it, hallucinogens distort perception and thinking, and opioids relieve pain.
• Mechanism and effect are two ways of describing the same drugs and can criss-cross: nicotine, caffeine, and cocaine are all stimulants with different mechanisms.
• With repeated use the brain adapts, leading to tolerance, possible addiction through the reward system, and withdrawal when use is cut back.

Key terms

psychoactive drugs

Drugs that affect behavior and mental processes, in part by changing how neurotransmitters work.

agonist

A drug that mimics a neurotransmitter and activates its receptors (e.g., heroin and opioids activating endorphin receptors; nicotine).

antagonist

A drug that reduces a neurotransmitter's effect, for example by blocking its receptors (e.g., caffeine blocking receptors for a sleep-promoting chemical).

reuptake inhibitor

A drug that blocks reuptake, leaving more neurotransmitter in the synapse longer (e.g., cocaine leaving more dopamine).

stimulants

Drugs that increase central nervous system activity, often making a person feel alert or energized (e.g., caffeine, cocaine).

depressants

Drugs that decrease nervous system activity, often making a person feel relaxed or sleepy (e.g., alcohol).

hallucinogens

Drugs that can distort perception and thinking (e.g., marijuana).

opioids

Drugs, such as heroin, that can relieve pain.

tolerance

Needing more of a drug over time to produce the same effect.

addiction

Compulsive drug use despite harmful consequences; drugs activate the reward system, and brain changes and learned associations can contribute.

withdrawal

Unpleasant symptoms, like a headache, when a person cuts back on a drug the brain has adapted to.

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