Psychoactive Drugs (College Board AP® Psychology): Revision Note

Effects of psychoactive drugs

• Psychoactive drugs are chemicals that alter brain chemistry to produce an altered state of consciousness

  • They do this by influencing neurotransmitter function at various points in the neural communication process

• Some behavioral and cognitive changes are due to the actual chemical effects of the drug

  • Other changes may be due to expectations about the drug, which is known as the placebo effect

• Psychoactive drugs influence neurotransmitter function in three main ways as:

  • agonists

  • antagonists

  • reuptake inhibitors

• Agonists are drugs that occupy receptor sites on the postsynaptic membrane and activate them, mimicking the effect of the natural neurotransmitter

  • Agonists encourage neural firing by making an action potential more likely

    • E.g. morphine acts as an agonist for endorphin receptors, mimicking the body's natural pain-relief response

• Antagonists are drugs that occupy receptor sites but do not activate them, blocking the natural neurotransmitter from binding

  • Antagonists discourage neural firing by preventing the natural neurotransmitter from having its effect

    • E.g. some antipsychotic medications act as dopamine antagonists, reducing excessive dopamine activity

• Reuptake inhibitors are drugs that block the reabsorption (reuptake) of neurotransmitters back into the presynaptic neuron after they have been released into the synaptic cleft

  • This keeps neurotransmitters active in the synapse for longer than usual, prolonging and intensifying their effect

    • E.g. many antidepressants (such as SSRIs) work by blocking the reuptake of serotonin, increasing its availability in the synapse

Categories of psychoactive drugs

• There are four categories of psychoactive drugs:

• Stimulants arouse the autonomic nervous system

  • Caffeine and cocaine both increase the production of dopamine, serotonin, and norepinephrine, producing feelings of alertness and energy

• Depressants slow down the autonomic nervous system

  • Alcohol decreases dopamine levels and inhibits neural arousal centers, leading to slurred speech, impaired judgment, and slowed reactions

• Hallucinogens cause sensory distortions

  • Marijuana may increase serotonin levels and can induce sensory synesthesia

    • This is where stimuli from one sense are experienced through another; perceptual alterations can sometimes be frightening

• Opioids act as agonists for the brain's endorphin receptors

  • Heroin, oxycodone, and codeine all activate these receptors, producing powerful pain relief and euphoria; opioids are among the most physically addictive psychoactive drugs

Dependence and tolerance

Tolerance

• With repeated use of a psychoactive drug, the brain adapts by reducing its sensitivity to the drug, meaning that increasingly larger doses are needed to achieve the same effect

  • Tolerance develops because the brain attempts to maintain normal functioning in the presence of the drug

  • Tolerance can develop to both the psychological and physical effects of a drug

Addiction

• Addiction is a state where a person has developed a compulsive need for a drug, both psychologically and physically

  • Psychological dependence occurs when an individual feels an intense desire or craving for the drug in order to function or feel a certain way

  • Physical dependence occurs when the body has adapted to the presence of the drug and requires it to function normally

• Many addictive drugs work by stimulating activity in the brain's dopaminergic reward pathway, producing intense feelings of reward and pleasure that reinforce continued drug use

Withdrawal

• When a person who has developed physical dependence stops taking a drug, they experience withdrawal symptoms

• Withdrawal symptoms are typically the opposite of the drug's effects, e.g.

  • A stimulant user may experience fatigue and depression during withdrawal

  • A depressant user may experience anxiety and agitation

• Withdrawal symptoms can range from uncomfortable to life-threatening depending on the drug and the degree of dependence

• The severity of withdrawal is one reason why addiction is considered a biological as well as a psychological condition