Phenobarbital for a dog that has seizures.?

I have a 5 yr old Pekingese that i notice seizure every 5-6 months. Took him to the vet & he was diagnose w/ epilepsy. He had lap work done & result came out clean. Vet suggested him to be on phenobarbital. What are the side effects? Would my dog personality change? I know that phenobarbital can cause severe liver damage. I am worried bout starting him on meds but I know that putting him on medication will help his seizures.