Psychology › Section D · States of consciousness › Topic D.5
Substance use and psychoactive drugs
From a morning coffee to a hospital painkiller, psychoactive drugs change consciousness by working on the brain's own chemical messengers. This topic explains how clinicians define a substance use disorder, how each major class of drug acts, and what the current evidence says. It is education, not a tool for diagnosing anyone.
In this topic
- Substance use disorder in DSM-5-TR
- Tolerance, withdrawal and dependence
- One map: agonists and antagonists
- Depressants: alcohol and sedatives
- Stimulants and dopamine
- Caffeine and nicotine
- Opioids
- Hallucinogens and cannabis
- Worked example: predicting withdrawal from the mechanism
- Worked example: weighing a cannabis headline
- Common mistakes to avoid
- Key takeaways
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