Prozac is a selective serotonin reuptake inhibitor antidepressant. It is capable of affecting the chemicals of the brain that become unbalanced and can cause medical issues that range from depression to anxiety to panic attacks and beyond. Prozac is one of the top antidepressants for treating both depression and anxiety disorders. As an SSRI, Prozac increases the presence of serotonin in the brain. Serotonin is a neurotransmitter that promotes better moods.