They don’t, unless it is sufficiently controlled by medication. A doctor has to sign off that they think you can drive safely. Regulations vary by jurisdiction. Here in Ohio, USA you get a two-part license that says you need a doctor’s permit every time you renew your license to say you can continue to drive. Then you carry a piece of the paper (the second part) with your DL.

For the doctor (neurologist) to be confident that you aren’t going to have seizure while driving, you have to have been seizure free for some time, plus maybe have regular EEG scans to confirm that you are not susceptible to seizures while being exposed to blinking lights. The blinking lights are part of the EEG scan. You basically hyperventilate (on purpose) while they flash lights at different frequencies and measure your brain waves. If the response is too severe, you fail.

Like any condition, epilepsy comes in many forms and many levels of severity. Some epileptics can barely function and can have brain damage from too many seizures. Some people have no effects at all as long as they are on medication.