Common side effects of phenobarbital in dogs include drowsiness, agitation, increased appetite, increased thirst and increased urination. (animals.mom.me)
When unacceptable side effects develop with phenobarbital use, the dose may be substantially cut back or even discontinued. (vin.com)
If the liver is larger than normal, but causing no pain it could be Cushing's disease, diabetes or from phenobarbital use. (dog-health-guide.org)