In most cases, you’ll have to use the medicines on your skin for 2 to 4 weeks to make sure you kill the fungus that causes ringworm. It’ll also lower the chances of it coming back.
If you have ringworm on your scalp or in many different places on your body, over-the-counter treatments may not be enough. Your doctor will write you a prescription for an antifungal medication that you’ll have to take by mouth for 1 to 3 months. You might also have to use an antifungal shampoo.