This medication is used alone or with other medications to control seizures. Controlling and reducing seizures lets you do more of your normal daily activities, reduces your risk of harm when you lose consciousness, and lessens your risk for a possibly life-threatening condition of frequent, repeated seizures. Phenobarbital belongs to a class of drugs known as barbiturate anticonvulsants/hypnotics. It works by controlling the abnormal electrical activity in the brain that occurs during a seizure. This medication is also used for a short time (usually no more than 2 weeks) to help calm you or help you sleep during periods of anxiety. It works by affecting certain parts of the brain to cause calming.

Take this medication by mouth with or without food as directed by your doctor, usually once daily at bedtime for seizure control. Take with food or milk if stomach upset occurs. If you are using the liquid form of this medication, measure the dose carefully using a special measuring device/cup. Do not use a household spoon because you may not get the correct dose.

The dosage is based on your medical condition, phenobarbital blood levels, and response to treatment. Children's dosage may also be based on weight.

Your doctor may direct you to start this medication at a low dose and gradually increase your dose to prevent side effects such as drowsiness and dizziness. Follow your doctor's instructions carefully. Do not take more or less of this drug than prescribed.

It may take several weeks to reach the best dose for you and completely control your seizures. This medication works best when the amount of drug in your body is kept at a constant level. Take it at the same time(s) each day.

Do not stop taking this medication (and other anticonvulsant medications) without consulting your doctor. Your seizures may worsen or cause a very severe seizure that is difficult to treat (status epilepticus) when this drug is suddenly stopped.

If you suddenly stop using this medication, you may have withdrawal symptoms (such as anxiety, hallucinations, twitching, trouble sleeping). Withdrawal from phenobarbital can be severe and include seizures and (rarely) death. To help prevent withdrawal, your doctor may lower your dose slowly. Withdrawal is more likely if you have used phenobarbital for a long time or in high doses. Tell your doctor or pharmacist right away if you have withdrawal.

Though it helps many people, this medication may sometimes cause addiction. This risk may be higher if you have a substance use disorder (such as overuse of or addiction to drugs/alcohol). Take this medication exactly as prescribed to lower the risk of addiction. Ask your doctor or pharmacist for more details.

When this medication is used for a long time for anxiety or to help you sleep, it may not work as well. Phenobarbital should only be used for a short time for anxiety or sleep. Talk with your doctor if this medication stops working well.

Tell your doctor if your anxiety or seizure control gets worse (such as the number of seizures increases).

Dizziness, drowsiness, excitation, headache, tiredness, loss of appetite, nausea, or vomiting may occur as your body adjusts to the medication. If any of these effects last or get worse, notify your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

A small number of people who take anticonvulsants for any condition (such as seizure, bipolar disorder, pain) may experience depression, suicidal thoughts/attempts, or other mental/mood problems. Tell your doctor right away if you or your family/caregiver notice any unusual/sudden changes in your mood, thoughts, or behavior including signs of depression, suicidal thoughts/attempts, thoughts about harming yourself.

Tell your doctor right away if you have any serious side effects, including:

• staggering walk/clumsiness
• double vision
• fainting
• slow heartbeat
• severe tiredness/weakness
• pale skin

Get medical help right away if you have any very serious side effects, including:

• slow/shallow breathing

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• fever
• swollen lymph nodes
• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

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.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug include:

• darunavir
• orlistat

Other medications can affect the removal of phenobarbital from your body, which may affect how phenobarbital works. Examples include St. John's wort, among others.

This medication can speed up the removal of other medications from your body, which may affect how they work. Examples of affected drugs include artemether/lumefantrine, asunaprevir, atazanavir, cobicistat, etravirine, lurasidone, ranolazine, rilpivirine, sofosbuvir, sorafenib, voriconazole, certain calcium channel blockers (such as felodipine/nimodipine), among others.

This medication may decrease the effectiveness of hormonal birth control such as pills, patch, or ring. This could cause pregnancy. Discuss with your doctor or pharmacist if you should use reliable backup birth control methods while using this medication. Also tell your doctor if you have any new spotting or breakthrough bleeding, because these may be signs that your birth control is not working well.

The risk of serious side effects (such as slow/shallow breathing, severe drowsiness/dizziness) may be increased if this medication is taken with other products that may also cause drowsiness or breathing problems. Tell your doctor or pharmacist if you are taking other products such as opioid pain or cough relievers (such as codeine, hydrocodone), alcohol, marijuana (cannabis), other drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), muscle relaxants (such as carisoprodol, cyclobenzaprine), or antihistamines (such as cetirizine, diphenhydramine).

Check the labels on all your medicines (such as allergy or cough-and-cold products) because they may contain ingredients that cause drowsiness. Ask your pharmacist about using those products safely.

Phenobarbital is very similar to primidone. Do not use medications containing primidone while using phenobarbital.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669. Symptoms of overdose may include: severe tiredness/dizziness, inability to wake up, very slow breathing rate.

Do not share this medication with others. Sharing it is against the law.

For long-term use, lab and/or medical tests (such as phenobarbital blood levels, blood counts, liver/kidney function) should be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

If you are taking this medication to prevent seizures and miss a dose, take it as soon as you remember unless it is almost time for the next dose. In that case, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.

Your condition can cause complications in a medical emergency. For information about enrolling in MedicAlert, call 1-888-633-4298 (US) or 1-800-668-1507 (Canada).