Turning dopamine down
The core action of almost every antipsychotic is to block a particular dopamine receptor, the D2 subtype. Acting as antagonists, they sit on the receptor so dopamine can't switch it on. In the brain pathway tied to psychosis, dialling dopamine down reduces hallucinations and delusions. The trouble is that dopamine matters in other pathways too — and blocking it there is the source of the side effects.
The most distinctive side effects are movement problems — stiffness, tremor, restlessness, and slowness — because the same dopamine block hits the brain's motor-control pathway. In effect, antipsychotics can produce a Parkinson-like state, the mirror image of the disease you will meet in guide 5. Blocking dopamine in yet another pathway raises the hormone prolactin, causing further unwanted effects.
Mood stabilizers and the narrow window
Bipolar disorder swings between mania and depression. A mood stabilizer dampens both extremes. Lithium is the classic example — a simple ion whose exact mechanism is still debated, yet which reliably reduces mania, prevents relapse, and lowers suicide risk. Some antiepileptics from guide 5 double as mood stabilizers, a reminder that calming over-excitable circuits helps in both seizures and mania.
Across all these drugs, the prescriber's job is matching indication to the least harmful option: enough dopamine block to control psychosis without disabling movement, enough lithium to steady mood without toxicity. The skill is balance, not maximum dose.