Phenobarbital is a barbiturate (bar-BIT-chur-ate). Phenobarbital slows the activity of your brain and nervous system.

Phenobarbital is used to treat or prevent seizures. Phenobarbital is also used short-term as a sedative to help you relax.

Phenobarbital may also be used for purposes not listed in this medication guide.

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.

Phenobarbital comes as a tablet and an elixir (liquid) to take by mouth. It is usually taken one to three times a day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take phenobarbital exactly as directed.

If you take phenobarbital for a long time, it may not control your symptoms as well as it did at the beginning of your treatment. Talk to your doctor about how you are feeling during your treatment.

Phenobarbital can be habit-forming. Do not take a larger dose, take it more often, or take it for a longer time than prescribed by your doctor.

Do not stop taking phenobarbital without talking to your doctor. If you suddenly stop taking phenobarbital, you may experience withdrawal symptoms such as anxiety, muscle twitching, uncontrollable shaking of a part of the body, weakness, dizziness, changes in vision, nausea, vomiting, seizures, confusion,difficulty falling asleep or staying asleep, or dizziness or fainting when getting up from a lying position. Your doctor will probably decrease your dose gradually.

Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Phenobarbital may be habit-forming. Never share phenobarbital with another person, especially someone with a history of drug abuse or addiction. Keep the medication in a place where others cannot get to it. Selling or giving away this medicine is against the law.

Do not change your phenobarbital dose without your doctor's advice. Tell your doctor if the medicine does not seem to work as well in treating your condition.

If you are taking phenobarbital to treat seizures, keep taking the medicine even if you feel fine.

Do not stop using suddenly after long-term use, or you could have unpleasant withdrawal symptoms. Ask your doctor how to safely stop using phenobarbital.

Store at room temperature away from moisture, heat, and light.

Keep track of the amount of medicine used from each new bottle. Phenobarbital is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.

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.

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenobarbital can be fatal.

Overdose symptoms may include slow or shallow breathing, weak pulse, cold or clammy skin, little or no urination, pinpoint pupils, feeling cold, or fainting.

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

Unless your doctor tells you otherwise, continue your normal diet.

Drinking alcohol with phenobarbital can cause side effects.

This medication may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Phenobarbital may cause a severe allergic reaction. Stop taking phenobarbital and get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, eyes, lips, tongue, or throat.

Phenobarbital may cause serious side effects. Call your doctor at once if you have:

• weak or shallow breathing;

• unusual pain anywhere in your body (especially in the neck, shoulder, or arms);

• a red blood cell disorder--pale skin, muscle weakness, diarrhea, weight loss, rapid heart rate, tongue swelling, numbness or tingling in your hands or feet, feeling short of breath; or

• severe skin reaction--fever, sore throat, swelling in your face or tongue, burning in your eyes, skin pain followed by a red or purple skin rash that spreads (especially in the face or upper body) and causes blistering and peeling.

Side effects such as confusion, depression, or excitement may be more likely in older adults and those who are ill or debilitated.

Common side effects of phenobarbital may include:

• drowsiness, lack of energy;

• dizziness or spinning sensation;

• depressed mood;

• feeling restless or excited (especially in children or older adults);

• drunk feeling; or

• "hangover" effect (drowsiness the day after taking phenobarbital).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Taking this medicine with other drugs that make you sleepy or slow your breathing can cause dangerous or life-threatening side effects. Ask your doctor before taking phenobarbital with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.

Other drugs may interact with phenobarbital, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your response to phenobarbital.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.