Tranylcypromine hemisulfate is primarily used as an antidepressant in the treatment of major depressive disorder, particularly in cases where other treatments have not been effective. It functions as a monoamine oxidase inhibitor (MAOI), which helps to increase the levels of certain chemicals in the brain that are responsible for mood regulation. This makes it especially useful for patients with atypical depression or those who have not responded well to other classes of antidepressants. Additionally, it is sometimes prescribed for anxiety disorders and certain types of phobias. Due to its potent action, it requires careful monitoring and adherence to dietary restrictions to avoid potentially severe interactions with certain foods and medications.