Serotonin selective reuptake inhibitors (SSRIs) are a type of antidepressant and, like any other drug, they can have side effects. One of the most worrying side effects is a cluster of symptoms sometimes referred to as activation syndrome. These symptoms can include: anxiety, agitation, panic attacks, insomnia, irritability, hostility, aggressiveness, impulsivity, akathisia (extreme restlessness and fidgitiness) and mania. Apart from being unpleasant in itself activation syndrome has also been linked to an increased risk of suicide. A Japanese study of 729 patients who had been prescribed antidepressants found that 4.3% of them developed activation syndrome. The incidence of activation syndrome was not associated with gender or age but it was linked to a diagnosis of personality disorder which quadrupled the risk.
Harada, Tsuyoto, Sakamoto, Kaoru and Ishigooka, Jun - Incidence and predictors of activation syndrome induced by antidepressants Depression and Anxiety December 2008, 25(12), 1014-1019