Common Side Effects

• Common side effects of phenobarbitol in dogs include drowsiness, loss of coordination or clumsiness, and excessive hunger, thirst and urination.
  
  

Time Frame

• Ordinarily, the common side effects of phenobarbitol occur during the first two weeks of use and gradually diminish once a dog adjusts to the medication, according to the Canine Epilepsy Resource Center.
  
  

Drug Interactions

• Combining the anxiety medication acepromazine with phenobarbitol increases the risk of serious side effects. Additionally, barbiturates may decrease the effectiveness of phenobarbitol, which could lead to a return of seizures.
  
  

Risks

• The most serious risk of phenobarbitol use in dogs is liver damage.
  
  

Solution

• Most veterinarians order regular blood work to determine if the liver is functioning properly, as prompt detection of a problem can help avoid permanent damage. In addition, milk thistle supplements may help protect a dog's liver from the medication, suggests the Canine Epilepsy Resource Center.