Citalopram, sold under the brand name Celexa among others, is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. It is used to treat major depressive disorder, obsessive compulsive disorder, panic disorder, and social anxiety disorder. The antidepressant effects may take one to four weeks to occur. It is typically taken orally. In some European countries, it is sometimes given intravenously to initiate treatment, before switching to the oral route of administration for continuation of treatment. It has also been used intravenously in other parts of the world in some other circumstances.