Antidepressant drug. Pills of Seroxat (paroxetine), an antidepressant drug. It belongs to a class of drugs known as selective serotonin re-uptake inhibitors (SSRIs), which also includes Prozac. Serotonin is a brain chemical that helps regulate moods, lack of which can lead to depression. SSRIs work by prolonging the action of serotonin by slowing its reabsorption by the brain. SSRIs are favoured to older antidepressants that are less selective and cause more side effects. Seroxat is also prescribed as a cure for shyness, although such use is controversial.