Neurobiology and Pharmacology of Substance Use
What to know
Understand the mesolimbic dopamine pathway (ventral tegmental area → nucleus accumbens) as the reward circuit, plus the role of the prefrontal cortex (impulse control) and amygdala (stress/craving). Know tolerance, dependence, withdrawal, and sensitization. Map drug classes to mechanisms: opioids (mu-receptor agonists), alcohol (GABA-A potentiation, NMDA antagonism), benzodiazepines (GABA-A), stimulants (dopamine/norepinephrine reuptake blockade), cannabis (CB1), nicotine (nicotinic acetylcholine receptors). Know half-lives and onset that drive withdrawal timing (short-acting agents cause earlier, more intense withdrawal). Understand cross-tolerance (alcohol and benzodiazepines both act on GABA-A) and kindling (repeated withdrawal worsens seizure risk).
Traps
Questions confuse pharmacokinetics (what the body does to the drug) with pharmacodynamics (what the drug does to the body). Watch for items implying dopamine is the "pleasure chemical" alone - it also drives wanting/craving and learning. Distinguish agonist (full activation), partial agonist (buprenorphine), antagonist (naloxone, naltrexone), and inverse agonist. Don't confuse disulfiram (blocks aldehyde dehydrogenase) with agents that reduce craving.
Rule of thumb
Withdrawal syndromes are generally the opposite of the drug's acute effect: alcohol (depressant) withdrawal is excitatory (tremor, seizures, autonomic surge); stimulant withdrawal is depressant-like (fatigue, anhedonia).
Worked example
A patient on chronic high-dose benzodiazepines stops abruptly and seizes. Mechanism: loss of GABA-A potentiation plus kindling and glutamate rebound - explaining why abrupt discontinuation of GABAergic drugs is dangerous and requires tapering.