Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressant medications primarily used in the treatment of depression, including major depressive disorder and other depressive conditions. They work by inhibiting the reuptake of serotonin in the brain, making more serotonin available for neurotransmission. While SSRIs may sometimes be used off-label for other conditions like anxiety disorders, their primary indication is in the treatment of depression. They are not the first-line treatment for bipolar depression (mood stabilizers are usually preferred), migraine (other specific medications are used), or schizophrenia (antipsychotics are the primary treatment).