Before taking phenobarbital, tell your doctor or pharmacist if you are allergic to it; or to other barbiturates (such as primidone, secobarbital); or to other anti-seizure medications (such as carbamazepine, fosphenytoin, oxcarbazepine, phenytoin); or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: certain hormone problems (adrenal disease such as Addison's disease), liver problems, kidney problems, lung disease (such as sleep apnea, chronic obstructive pulmonary disease-COPD), mental/mood disorders (such as depression, thoughts of suicide), personal or family history of a substance use disorder (such as overuse of or addiction to drugs/alcohol), personal/family history of a certain blood disorder (porphyria), certain vitamin deficiencies (folic acid, vitamin K).

This drug may make you dizzy or drowsy. Alcohol or marijuana (cannabis) can make you more dizzy or drowsy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Avoid alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

The liquid form of this product may contain alcohol or sugar. Caution is advised if you have diabetes, alcohol dependence, liver disease, or any other condition that requires you to limit/avoid these substances in your diet. Ask your doctor or pharmacist about using this product safely.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Older adults may be more sensitive to the side effects of this drug, especially drowsiness and dizziness. However, this drug can often cause excitement or confusion instead of drowsiness in older adults. Drowsiness, confusion, and dizziness can increase the risk of falling.

Children may be more sensitive to the side effects of the drug. This drug can often cause excitement instead of drowsiness in young children.

During pregnancy, this medication should be used only when clearly needed. It may harm an unborn baby. Newborn babies of mothers who use this medication late in pregnancy may have symptoms such as slow/shallow breathing, nonstop crying, shaking, or trouble feeding. However, since untreated seizures are a serious condition that can harm both a pregnant woman and her unborn baby, do not stop taking this medication unless directed by your doctor. If you are planning pregnancy, become pregnant, or think you may be pregnant, discuss with your doctor right away the benefits and risks of using this medication during pregnancy. Since birth control pills, patches, implants, and injections may not work if taken with this medication (see also Drug Interactions section), discuss reliable forms of birth control with your doctor.

This medication passes into breast milk and may cause excessive sleepiness or feeding problems in the nursing infant. Consult your doctor before breastfeeding.