The advantages of phenobarbital are its long history of use, low cost, and effectiveness. It stays in the body for a long time, so the amount of medicine in the blood stays fairly steady even if it is taken only once a day.

A disadvantage is that it makes many people sleepy and sometimes causes other changes in behavior. Not everyone is affected the same way, however, and many individuals do well when they take phenobarbital. Another problem is that after people take it for a while, they must be very careful if they want to stop taking it. They could have withdrawal seizures. The doctor will recommend a very slow reduction in the dose to prevent these seizures.

The same medicine is available in several forms because people's needs vary. The name or appearance may differ from country to country, or even from manufacturer to manufacturer, but usually the dose (measured in milligrams, abbreviated "mg") will be the same. In the United States, several companies sell phenobarbital, in these forms:

Phenobarbital (fee-no-BAR-bih-tal) is a seizure medicine manufactured by several companies. It is the oldest epilepsy medicine still in use. In 1912, two independent teams of chemists created it under the name of Luminal.


Updated: 06/06/2024

Brand Name(s)


Used to Treat

Lennox-Gastaut Syndrome
Rasmussen’s Syndrome
Temporal Lobe Epilepsy
Clonic Seizures
Focal Impaired Awareness or Complex Partial Seizures
Refractory Seizures
Secondarily Generalized Seizures or Bilateral Tonic Clonic Seizure
Focal Aware Onset Seizure
Tonic Seizures
Tonic-clonic Seizures


15mg Phenobarbital


30mg Phenobarbital


60mg Phenobarbital


100mg Phenobarbital


Liquid Solution

20 mg per 5 mL (milliliters)

Package Insert

Frequently Asked Questions

    How to take and store Phenobarbital?

    It's OK to take phenobarbital either with food or without food, but it's best to be consistent from day to day. Follow the doctor's directions. Call if you have any questions. The way the medicine is taken depends, of course, on what form the doctor has prescribed.

    Phenobarbital is usually taken just once a day. Most people find that sleepiness is less of a problem during the day if they take the phenobarbital 30 to 60 minutes before bedtime.

    If needed, tablets may be crushed and put in foods for children. A liquid (elixir) is available for those who cannot swallow pills, however. This liquid can be given with water, milk, or juice. Be sure to use the same standard-size medicine spoon or dropper each time to get an accurate dose.

    If the doctor changes the amount of phenobarbital to be taken, you may be given a different form. For example, you may start out using 30-mg tablets and then switch to 60-mg tablets. If this happens, be careful to use the correct number. Don't automatically continue to use the same number of pills as before.

    Store phenobarbital at room temperature, away from heat, direct light, and dampness. If you have the liquid form, prevent it from freezing. Be particularly careful to keep phenobarbital out of the reach of children, since overdose is especially dangerous for children.

    Don't use more than the doctor prescribes. If one or two extra tablets or an extra spoonful of liquid are taken, call the doctor for advice. For a larger overdose, call your local poison control center or emergency room right away unless you have other specific directions from your doctor.

    Don't stop using phenobarbital or change the amount taken without talking to the doctor first. Stopping any seizure medicine all at once can affect other medicines in the body. It may even cause nonstop seizures that can be life-threatening.

    What if I forget?

    Ask the doctor what to do if you forget a dose. In general, a forgotten dose should be taken right away, unless it is almost time for the next one. In that case, just use one dose—not a double dose—and call the doctor's office for more advice.

    Do your best to follow the doctor's directions. If you forget doses often, it may be a good idea to get a special pillbox or watch with an alarm to remind you.

    Taking the amount of seizure medicine the doctor prescribes and taking it at the right time every single day are the most important steps in preventing seizures!

    How well does the Phenobarbital work?

    Phenobarbital has been used to treat epilepsy since the early decades of the 20th century. It is still commonly used throughout the world because it is both effective and low in cost. Also, most people need to take it only once a day, so they are less likely to miss doses.

    Phenobarbital is useful in controlling focal aware (formally called simple partial), focal impaired awareness (formerly called complex partial), and generalized tonic-clonic seizures in patients of all ages. It has often been considered the first choice to treat certain kinds of seizures in infants.

    In studies of seizure medicines, some people do better with phenobarbital and others do better with something else. It's difficult to forecast the results for any given person. Differences in side effects may be important in deciding which medicine is best for each person.

    Some doctors hesitate to prescribe phenobarbital because it has a reputation for causing unwanted side effects, especially sleepiness in adults and problems with behavior or learning in children. Side effects are much more likely to be troublesome if a high dose is given, especially at the beginning. It may be necessary to increase the amount used very slowly over several months. Side effects are more common when phenobarbital is first taken or when the dose is increased, but not everyone is affected and some people can take high doses without trouble.

    If seizures continue, the doctor probably will change the amount of phenobarbital prescribed. If that doesn't work, the next step may be either to prescribe a different seizure medicine by itself or to prescribe a combination of phenobarbital and another seizure medicine. Many are available. No single combination is best for everyone. Phenobarbital is often used as an "add-on" medicine for people who continue to have seizures while taking other seizure medicines. It does interact with many other medicines, so the amount taken may need to be adjusted if a combination is used.

    What are the most common side effects of Phenobarbital?

    Doctors have been able to study and observe the side effects of phenobarbital for many years. In some ways this is an advantage over new medicines. Many doctors no longer prescribe it unless other seizure medicines have failed, however, because of concern that its side effects often outweigh its benefits (except for certain groups such as very young children). It may be used more frequently in situations where cost is a critical issue, such as in developing countries.

    The most common side effect of phenobarbital is sleepiness or fatigue. Be careful with driving, operating machinery, or any other dangerous activity until you know how you react to phenobarbital.

    Other side effects include:

    • depression
    • hyperactivity (in children)
    • trouble paying attention (in children and adults)
    • dizziness
    • memory problems
    • decreased sexual interest
    • for males, inability to have an erection
    • slurred speech
    • upset stomach
    • anemia
    • deficiency of the vitamin folic acid
    • rash
    • fever
    • low calcium levels, bone loss

    If you notice problems like any of these while you are taking phenobarbital, it's probably a good idea to discuss them with your doctor or nurse. You shouldn't stop taking phenobarbital or any other seizure medication without your doctor's advice.

    Phenobarbital also has been found to reduce the effectiveness of oral contraceptives (birth control pills), so women who could become pregnant may want to consider another form of birth control.

    Some studies have found greater problems with behavior and thinking in children taking phenobarbital than in children taking other seizure medicines. Not all the results agree, however, perhaps because individual children are affected differently.

    Taking extra calcium and vitamin D may help to prevent bone loss. If you have been taking phenobarbital for more than 5 years, it might be a good idea to have a bone density test. If this easy, painless test shows thinning of your bones, your doctor may want you to see a specialist.

    Be sure to read about the more serious side effects of phenobarbital. Serious problems are very rare but everyone who takes this medicine should be aware of them.

    Long-term effects
    Long-term use of phenobarbital can lead to changes in the soft tissues of the body. Symptoms include pains in the joints or thickening in areas such as the palm or the bottom of the foot. If you notice any changes of this kind, tell the doctor.

    What are the most serious side effects of Phenobarbital?

    Phenobarbital has a long history of safe use. However, more serious side effects do occur once in a while and should be discussed with your doctor.

    Phenobarbital belongs to a group of medicines that can be addictive. People who take it to treat epilepsy hardly ever become psychologically addicted, but they are likely to experience physical dependence. With physical dependence, withdrawal symptoms occur if the medication is stopped suddenly or if the amount taken is sharply reduced. These withdrawal symptoms may include:

    • anxiety
    • increased heart rate
    • sweating
    • confusion
    • seizures
    • death (very rarely)

    Withdrawal symptoms can be avoided or greatly reduced by lowering the amount used very slowly over a long time.

    Depression is also a side effect, those who have experienced depression, drug abuse, or suicidal tendencies in the past should be especially careful with this medicine.

    Women who may become pregnant should discuss the effects of phenobarbital with their doctor. It may be more likely than some other seizure medicines to cause birth defects, and there is a danger that the baby may experience withdrawal symptoms if the mother takes phenobarbital in the last few months of pregnancy. Since phenobarbital reduces the effectiveness of oral contraceptives (birth control pills), women should be especially cautious.

    In general, it is wise to avoid alcohol while taking phenobarbital. Adults with a responsible approach to drinking (and who are taking a low to medium dose of phenobarbital) may want to talk to the doctor about the possibility of having a drink or two occasionally. Some doctors recommend that phenobarbital should never be combined with alcohol, narcotics, tranquilizers, or antihistamines. You might fall into a coma or die if, for example, you drank a large amount of alcohol in one night while taking a high dose of phenobarbital.

    Finally, it's not unusual for phenobarbital to make people feel sleepy or uncoordinated. If you've just started taking phenobarbital or have just started taking a larger dose, be careful about doing things that could be dangerous until you know how it will affect you.

    On July 10, 2008, an advisory panel was convened by the Food and Drug Administration (FDA) to review data that the FDA had previously collected from drug studies showing an association between many of the antiepileptic drugs (AEDs) and suicidal ideation and behavior, which together are called suicidality. According to the FDA's Alert, among the patients with epilepsy in these drug studies, 1 out of 1000 people taking the placebo (inactive substance) showed suicidality compared to approximately 3.5 out of 1000 people who took an AED. The FDA advisory panel voted to accept the FDA's data at its meeting on July 10.

    • Taking antiepileptic medicines may increase the risk of having suicidal thoughts or actions;
    • Do not make any changes to the medication regimen without first talking with the responsible healthcare professional;
    • Pay close attention to any day-to-day changes in mood, behavior and actions. These changes can happen very quickly so it is important to be mindful of any sudden differences.
    • Be aware of common warning signs that might be a signal for risk of suicide. Some of these are:
      • Talking or thinking about wanting to hurt yourself or end your life
      • Withdrawing from friends and family
      • Becoming depressed or having your depression get worse
      • Becoming preoccupied with death and dying
      • Giving away prized possessions

    We again urge patients and families to contact their doctor before stopping an epilepsy medication because this may possibly lead to seizures and worsening of mood.

    Can Phenobarbital be taken with other medicines?

    Sometimes one kind of medicine changes the way another kind of medicine works in the body. This is true not only for prescription medicines, but also for medicines you just pick up off the shelf at the store. It's also true for herbal products, vitamins, a few kinds of food, and even cigarettes!

    Any time a doctor suggests a new prescription, be sure to talk about what other medicines you are already using. If two kinds of medicine affect each other, the doctor may want to prescribe something else or change the amount to be taken.

    Taking phenobarbital will lower the level in the blood of several other seizure medicines:

    • Tegretol, Carbatrol (carbamazepine)
    • Lamictal
    • Zonegran
    • Gabitril
    • Depakote, Depakene (valproic acid)

    Medicines often used for other disorders are also affected. It is especially important to check with your doctor before taking any of these:

    • Antidepressants
    • Allergy medicines
    • Coumadin (warfarin)
    • Theophylline
    • Tagamet (cimetidine)
    • Oral contraceptives (birth control pills)
    • Narcotic pain relievers such as Percocet
    • Sedatives such as Nembutal and Seconal
    • Steroids such as Medrol and Deltasone
    • Tranquilizers such as Xanax and Valium
    What are the effects of Phenobarbital on Children?

    Phenobarbital is useful in treating many kinds of seizures in children. It is often considered the first choice to treat certain seizures in newborn infants.

    Phenobarbital also has been widely used to prevent seizures that sometimes accompany a high fever in infants or young children. It does not enter the body quickly enough to prevent these seizures if it is only given after the fever starts, however, so the child must take it every day. Seizures of this kind usually cause no lasting harm, so most children should not be given phenobarbital to prevent them.

    Phenobarbital has a reputation for causing problems with behavior or learning in children. Reports from various studies have not always agreed, perhaps because individual children are affected in different ways. The problems are probably not as serious for most children as many doctors think they are, but other seizure medicines may be preferred as a first choice for long-term use in children.

    Side effects are much more likely to be troublesome if high doses are given or if too high a dose is given to start. It may be necessary to increase the dosage very slowly over several months. The doctor will calculate the dosage for a child based on the child's weight.

    If a woman takes Phenobarbital during pregnancy will it hurt the baby?

    Birth defects are probably a bit more common in the babies of women who take phenobarbital during pregnancy than in others. A large majority of women who take phenobarbital do have healthy, normal babies, however. The risk of defects is higher for women who take more than one seizure medicine. Women with a family history of birth defects also have a higher risk.

    There also is a danger to the baby from withdrawal symptoms if the mother takes phenobarbital in the last few months of pregnancy, since it crosses into the baby.

    All women who are capable of becoming pregnant should take at least 0.4 mg (400 mcg) of the vitamin called folic acid every day because it helps to prevent one type of birth defect. (The most well-known of these is spina bifida, in which the spinal cord is not completely enclosed.) These defects are more common in the babies of women who take phenobarbital during the first 4 to 6 weeks of pregnancy. If the doctor thinks a woman is at especially high risk, a much larger dose of folic acid—4 mg (4000 mcg) per day—may be recommended.

    Talk with your doctor about the potential effects of phenobarbital if you are pregnant or plan to become pregnant. Taking more than one seizure medicine may increase the risk of birth defects, so doctors sometimes gradually reduce the number or amount of seizure medicines taken by women planning for pregnancy. This is not always done, however, because it increases the risk of seizures. Some kinds of seizures can injure the baby, so do not stop using seizure medicines or reduce the amount without the doctor's OK.

    Because phenobarbital reduces the effectiveness of birth control pills, women who take it need to be especially cautious about pregnancy.

    What are the dose ranges for Phenobarbital?

    The best amount is the amount that completely controls seizures without causing troublesome side effects. It depends on many factors, which are different for every individual. Follow the doctor's directions. Call if you have any questions.

    An uncommon but serious side effect of phenobarbital is a possibility of becoming addicted to the medicine. Therefore, it is important to take only the amount that the doctor prescribes.

    No one should stop taking phenobarbital or change the amount they take without talking to the doctor first. Stopping any seizure medicine all at once can cause seizures that may be life-threatening. The risk of withdrawal symptoms with phenobarbital makes it especially important to be careful in stopping this medicine.

    Read About Phenobarbital studies

    In the United States, companies that manufacture medicines are required to publish certain kinds of information about each product. This document is commonly known as a “package insert” because it is usually included with each package of the medicine.

    You can also read these documents (also called "prescribing information") online. The U.S. package insert for phenobarbital is found at:

    Some of the information may differ in other countries.

    The summary of package characteristics can be obtained in any European language from:

    Find out how to read and understand a package insert.


    Primary Generalized Epilepsy

    Sign Up for Emails

    Stay up to date with the latest epilepsy news, stories from the community, and more.