Celexa is a medication available in tablet form, with strengths of 5mg, 10mg, 20mg, and 40mg. Its active ingredient, citalopram, is commonly used to treat depression by enhancing mood and overall well-being. Classified as a selective serotonin reuptake inhibitor (SSRI), Celexa functions by restoring the balance of serotonin in the brain, a natural substance that affects mood. It is also marketed under the names Citopam and Citacan.