What are the good and bad side affects of this drug? How can i overcome any side affects? ## HI, Rex! How are you? Phenytoin is an antiepileptic, so preventing seizures would be the good effect of it. Side effects may include nausea, dizziness, horizontal gaze nystagmus and reduced folic acid levels. Overcoming the side effects is really just a matter of time, as most will taper off in severity as your body gets used to the medication, which can take about 4 to 6 weeks. Learn more Phenytoin details here.