(Depression is thought to be due to insufficient ammounts of neurotransitters like serotonin being produced in the nerve endings (synapse). In noral brains, neurotrasmitters are constantly being released from nerve endings, stimulating the neighbouring neurons . To terminate their action , neurotransmitters are reabsorbed into the nerve endings and broken down by an enzyme.)
Antidepressants work by reducing the rate of reabsorption, or by blocking the enzyme that breaks down the neurotransmitters. Both of these mechanisms increase the ammount of neurotransmitter available to excite neighbouring cells.
The most commonly prescribed antidepressant drugs are selective seretonin reuptake inhibitors or SSRIs, such as Prozac.They work by blockig the transporter mechanism that reabsorbs serotonin into the presynaptic cel after it has fired so more of the serotonin is left in the synapse, prolonging it's activity and making transmission of the next impulse easier. Patients taking SSRIs are twice as likey to commit suicide (Ferguson et al, 2005)
(A patient with a psychotic mental dissorder like schizophrenia has lost touch with reaity and has little insight into their condition)
Conventional antipsychotics (like chloroproazine, brand name Largactil) combat the positive symptoms of schizophrenia . They block the action of neurotransmitter dopamine in the brain by binding to, but not stimulating dopamine receptors.
The atypical antipsychotic drugs (like clozapine, brand name Czaril) temporarily occupy dopamine receptors, then rapidly dissociate to allow normal dopamine transmission. This may explain the high level of side effects like Tarive dyskinesia (involuntary mouth and tongue movement) compared to conventional antipsychotics.