Hello Thank You for contacting HCM. finasteride is a type of steroid reductase inhibitor. It works by reducing the amount of the hormone dihydrotestosterone in the body. This makes the prostate gland smaller, which helps to relieve urinary problems. Most common side effects includes: -Chills -cold sweats -confusion -dizziness, faintness, or lightheadedness when getting up from a lying or sitting position Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. Wishing you good health.