You should not use phenobarbital if you have severe liver disease, severe asthma or COPD, a personal or family history of porphyria, or a history of addiction to drugs similar to phenobarbital.
Before taking this medicine
You should not take  phenobarbital if you are allergic to phenobarbital or other barbiturates (Nembutal, Seconal, and others), or if you have:
severe asthma, chronic obstructive pulmonary disorder (COPD), or other breathing disorder;
a personal or family history of porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system);
severe liver disease; or
a history of addiction to phenobarbital or similar medicines (Valium, Xanax, Ativan, and others).
To make sure phenobarbital is safe for you, tell your doctor if you have:
liver disease;
temporary or chronic pain;
a pituitary gland disorder;
pheochromocytoma (tumor of the adrenal gland);
kidney disease;
a food or drug allergy;
a condition for which you take a blood thinner (warfarin, Coumadin, Jantoven).
Follow your doctor's instructions about taking seizure medication if you are pregnant. Seizure control is very important during pregnancy, and having a seizure could harm both mother and baby. Do not start or stop taking this medicine without your doctor's advice, and tell your doctor right away if you become pregnant.
Phenobarbital can make birth control pills less effective. Ask your doctor about using a non-hormonal birth control (condom, diaphragm with spermicide) to prevent pregnancy.
It is not known whether phenobarbital passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.
