Although the precise mechanism of action of antidepressants is largely unknown, all currently used antidepressants increase the availability of brain monoamines. They exert this effect by various mechanisms, including monoamine reuptake inhibition, blocking of degradation enzymes or receptor blocking. Although there are major similarities across same class of antidepressants, each antidepressant has unique pharmacological characteristics. Antidepressants differ in their propensity to induce sedation, sexual dysfunction, gastrointestinal disturbance, weight changes, insomnia and other reactions. Small differences in pharmacology might become significant in particular patients. Given the variety of second-generation antidepressants, clinicians can choose optimal treatment, based on most prominent symptoms and comorbid conditions.

Antidepresivi koje se danas koriste u liječenju depresije povećavaju raspoloživost monoamina. Taj učinak postižu na različite načine, najčešće sprječavanjem ponovne pohrane monoamina, blokadom enzima za razgradnju, ili blokadom receptora. Iako antidepresivi unutar iste skupine imaju mnogo sličnosti, svaki antidepresiv ima jedinstvena farmakološka svojstva. Među antidepresivima postoje razlike u izazivanju sedacije, seksualnih disfunkcija, probavnih smetnji, promjena u tjelesnoj težini, nesanice, te drugih različitih reakcija. Male razlike u farmakologiji mogu biti vrlo značajne u nekih bolesnika. Stoga, kliničari mogu danas između različitih antidepresiva odabrati najbolju terapiju za pojedinog pacijenta, uzimajući u obzir dominantne simptome i druga komorbidna stanja.