Tricyclic antidepressants (TCAs) are a class of medications used primarily to treat depression. They work by increasing the levels of certain neurotransmitters, such as serotonin and norepinephrine, in the brain, which can help improve mood and alleviate symptoms of depression. TCAs are often prescribed when other antidepressants, like SSRIs, are not effective. In addition to depression, TCAs can also be used to treat conditions like anxiety disorders, chronic pain, and insomnia. Common side effects may include dry mouth, drowsiness, and weight gain. Due to their side effects and potential for overdose, TCAs are typically prescribed with caution.