Retin A (tretinoin) for acne. Retin a (tretinoin) is a great medication for acne but it is very strong! the first rule is to use it sparingly, more is not better. A pea sized drop is all you need for your whole face. Initially it will make you dry, red and flakey, but it helps dry out and calm down the oils glands. Use it before bed and not in the am, it will make your skin more sensitive to sunlight. Wear sunscreen!