Retin-A (tretinoin) is a retinoid medication that's used to treat acne in adults and children 12 years and older. It's available as a cream or a gel that's applied onto the skin once a day. Side effects include skin irritation, redness, and peeling. Your acne might get worse at the beginning of treatment, but it should get better as you continue using the medication. You must have a prescription for Retin-A (tretinoin) from your primary care provider or dermatologist; this medication isn't available over the counter.