Seroxat antidepressant pills. Blisterpack of pills of the antidepressant drug Seroxat (paroxetine hydrochloride). This belongs to a class of drugs known as selective serotonin re-uptake inhibitors (SSRIs), which also includes Prozac (fluoxetine). Serotonin is a brain chemical which helps regulate moods, lack of which is thought to lead to depression. SSRIs work by reducing the amount of serotonin destroyed by the brain, increasing the active life of the existing reserves. SSRIs cause less side effects than older antidepressants, which are far less selective. This drug has also been prescribed as a cure for shyness, although such use is controversial.