What is discontinuation syndrome and which antidepressants cause it?

Discontinuation syndrome occurs when antidepressants are stopped abruptly or tapered too quickly, causing flu-like symptoms, insomnia, nausea, dizziness, sensory disturbances described as "brain zaps," irritability, and anxiety. It is most common with short-acting SSRIs like paroxetine and SNRIs like venlafaxine because their blood levels drop rapidly. Fluoxetine rarely causes discontinuation syndrome because its active metabolite has a very long half-life of four to six days. The syndrome is not addiction but a physiological adjustment to reduced serotonin activity.