Phenobarbital is an anticonvulsant that vets prescribe off-label to treat seizures and epilepsy in dogs and in cats. It’s usually given twice a day, but the specific dosage depends on your pet’s weight. Phenobarbital commonly comes as tablets. But it can also be made into a liquid, oral paste, chewable treat, or topical gel to make it easier for your pet to take. The injectable form is mainly used by vets. Common side effects are sleepiness, hunger, thirst, and more frequent urination. Phenobarbital is a controlled substance that can be habit-forming for pets with long-term use.