Antidepressants

Mechanisms by class

Antidepressant classes act through distinct monoamine mechanisms - SSRIs (selective serotonin reuptake inhibition), SNRIs (combined serotonin/noradrenaline reuptake inhibition), tricyclics (broader monoamine reuptake inhibition plus additional receptor effects explaining their broader adverse effect profile), and MAOIs (monoamine oxidase inhibition, now rarely first-line given interaction/dietary restriction burden) - mechanism explains both efficacy and characteristic adverse effect/interaction risk
Reuptake inhibition increases synaptic monoamine availability, but clinical antidepressant effect typically lags behind this immediate pharmacological action by 2-4 weeks - reflecting downstream neuroadaptive changes (receptor sensitivity changes, neurotrophic effects) as the actual mechanism of therapeutic benefit, not the acute reuptake blockade itself

Amongst the most widely prescribed medication classes globally given the high prevalence of depressive and anxiety disorders

Regular clinical review during the initial weeks of treatment, particularly monitoring for early worsening of suicidal ideation (a recognised risk, especially in younger patients, in the initial weeks before mood benefit is established)
Serotonin syndrome risk assessment when combining serotonergic agents (SSRIs/SNRIs with MAOIs, tramadol, or other serotonergic drugs) given the potentially life-threatening interaction

Discontinuation should be gradual (tapered), not abrupt, particularly for shorter half-life agents (e.g. paroxetine, venlafaxine), given discontinuation syndrome risk (flu-like symptoms, sensory disturbances, mood disturbance) distinct from relapse of the underlying condition
MAOIs require strict dietary tyramine restriction and drug interaction avoidance given hypertensive crisis risk, explaining their now-limited first-line use despite comparable efficacy in some populations

Serotonin syndrome (a life-threatening interaction risk), SSRI/SNRI discontinuation syndrome, early suicidality risk in younger patients starting treatment, MAOI dietary/drug interaction restrictions (tyramine, hypertensive crisis)

Antidepressant discontinuation syndrome is distinct from relapse of the underlying depressive/anxiety disorder - it typically develops within days of stopping or rapidly tapering (particularly shorter half-life agents) and resolves with symptom overlap that can be mistaken for the original condition returning, making a gradual taper the standard approach to discontinuation

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