Mysoline was introduced for epilepsy in the 1950s. It remains a well-known medication but it is used by only a small percentage of people with epilepsy. Although it is very effective, side effects may decrease its value.

Mysoline (MY-soh-leen) is the brand name used in the United States, Canada, and many other countries for the seizure medicine with the generic name primidone (PRIM-ih-dohn).


Updated: 11/03/2022

Brand Name(s)

Mysoline is manufactured in the United States by Valeant Pharmaceuticals. The name or appearance may differ in other countries. The dose (measured in milligrams, abbreviated "mg") will usually be the same. The following descriptions apply to the U.S. versions:

Used to Treat

Juvenile Myoclonic Epilepsy
Myoclonic Seizures
Tonic-clonic Seizures



50-mg white, square-shaped tablet embossed with "M" and "Mysoline 50"


250-mg yellow, square-shaped tablet embossed with "M" and "Mysoline 250"

Generic primidone made by other companies is also available in the United States, in the same doses.

Both sizes of Mysoline tablets are scored so they can be cut in half easily if 125 mg is prescribed.

In Canada, primidone is available in 125-mg chewable tablets (Apo-Primidone) (not shown).

Package Insert

Frequently Asked Questions

    How to take and store Primidone?

    Swallow each tablet whole. Don't bite or chew it.

    Mysoline can be taken either with food or without food, but it's important to be consistent day in and day out. People who usually take Mysoline with food should try to do that all the time, because it affects the way the medicine is used by the body.

    Be careful if the doctor writes a new prescription using a different kind of pill. For example, if you've been using 50-mg tablets and the new prescription is for 250-mg tablets, be careful to use the correct number. Don't automatically continue to use the same number of pills as before.

    Store Mysoline tablets at room temperature, away from light and moisture and out of the reach of children.

    What if I forget?

    A forgotten dose should be taken right away. If it is almost time for the next dose, 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 right amount of seizure medicine on time every single day is the most important step in preventing seizures!

    How well does the Primidone work?

    Although not prescribed very often by doctors, Mysoline (primidone) can be effective in treating seizures. When Mysoline is consumed it is metabolized (processed by the body) into phenobarbital and phenoethylmelanamide, both of which have antiepileptic effects. Therefore, taking Mysoline gives you the effectiveness of phenobarbital plus additional protection. A patient whose seizures have not been controlled by phenobarbital may have better results from Mysoline.

    The most important study of Mysoline (primidone) looked at 622 adults who had partial seizures or secondarily generalized tonic-clonic seizures. Each person was treated with one of four medications. The four were primidone, phenobarbital, carbamazepine (Tegretol or Carbatrol), and phenytoin (Dilantin, Phenytek). Overall, the patients who took primidone were more likely to stop taking it because of intolerable side effects than those who took the other medicines. After the first month, however, there was hardly any difference in this regard between the primidone and the carbamazepine or phenytoin.

    The patients in this study who had tonic-clonic seizures achieved similar control from all four medications. Of those in this group who took primidone for a year, 63% were seizure-free. Patients were more likely to continue to take carbamazepine (Tegretol, Carbatrol) than the other medications when considering both seizure control and side effects, but Mysoline can be very effective for partial seizures.

    A similar study in children—which also included Depakote (valproate)—focused on the rate of side effects. Only 8% of the children who were given Mysoline had to stop taking it because of side effects. Phenobarbital, which can be an excellent medication, often is avoided in children because of the possibility of mental slowing. By using Mysoline alone, children can enjoy many of the same benefits while avoiding this problem because the amount of phenobarbital produced by breaking down the Mysoline is low.

    Mysoline is most often used as add-on therapy in adults whose seizures are not well controlled by other medications. It is frequently paired with carbamazepine (Tegretol or Carbatrol) or phenytoin (Dilantin, Phenytek).

    It is important to remember that no single combination of antiepileptic medications is perfect for everyone. Sometimes, a series of combinations must be tried before finding what is best for the individual patient.

    What are the most common side effects of Primidone?

    While many people who take Mysoline (primidone) don't report any side effects there are those who do. The most common complaints amongst those who do are:

    • unsteadiness
    • the feeling that the surroundings are spinning (vertigo)
    • irregular eye movements
    • nausea
    • vomiting
    • blurred or double vision
    • drowsiness
    • depression

    The problems are mild to moderate and usually disappear with time or when the dose is reduced.

    Some other side effects mentioned even less often are:

    • loss of appetite
    • irritability
    • acne or other skin lesions
    • sexual impotency
    • decreased sexual desire
    • blood abnormalities
    • frozen shoulder

    If these problems do not go away within several days, or are really bothersome, call the doctor. Sometimes the doctor can help with these side effects by changing the prescription:

    • reducing the overall amount of Mysoline
    • changing the amount taken at certain times, such as taking a greater proportion of the Mysoline at bedtime to reduce daytime sleepiness
    • prescribing smaller doses, to be taken more often

    No one should stop taking Mysoline or change the amount they take or when they take it without their doctor's guidance.

    People who have just started taking Mysoline (or who have just started taking a larger amount) should be careful during activities that might be dangerous, until they know whether they are having any side effects.

    Be sure to read about the more serious side effects so you will be aware of symptoms that might indicate the beginning of a serious reaction to Mysoline. These serious problems are very rare but everyone who takes this medicine should at least be aware of them.

    What are the most serious side effects of Primidone?

    Most people who take Mysoline (primidone) have no side effects or mild side effects that go away with no lasting harm, but a very small number of people have serious reactions. Here's a list of symptoms that may be the start of one of these problems. If you notice any of these symptoms, call your doctor right away:

    • An allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives)
    • Fever, swollen glands, sore throat, or sores in the mouth (could mean a blood problem)
    • Red or purple point-like rash or blistering or peeling skin lesions
    • Easy bruising, paleness, weakness, or fatigue
    • Worsening of seizures

    It's not unusual for Mysoline to make people feel sleepy or uncoordinated. If you've just started taking Mysoline or have just increased your dosage (especially if you tend to be sensitive to medications), be careful when doing things that could be dangerous (such as driving or using sharp objects) until you know how it will affect you.

    People who are taking Mysoline should avoid drinking alcohol because this combination can cause deep sedation or sleepiness.

    A complete list of all reactions to Mysoline can be found in the package insert, but it is important to remember that most people who take it have none of these serious problems.

    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.

    What else is Primidone used for?

    Often doctors find that medicines are useful for more than one purpose. It is legal to prescribe medicines for "off-label uses" even though the U.S. Food and Drug Administration (FDA) has not formally approved such use. Besides epilepsy, one off-label use of Mysoline is the treatment of tremors—specifically, essential tremor (ET), the most common movement disorder.

    Who should not take Primidone?

    People who have had a condition called porphyria should not take Mysoline (primidone). Furthermore,those who are sensitive to phenobarbital are advised to avoid it, because the body produces phenobarbital when it processes Mysoline.

    Women who are pregnant or may become pregnant, and those who are breast-feeding should be cautious about using Mysoline. The manufacturer suggests that breast-feeding be discontinued if the baby is unusually sleepy. Other seizure medicines may be a better choice for pregnant women and nursing mothers.

    What are the dose ranges for Primidone?

    Since Mysoline must be introduced gradually, the doctor will start by giving the patient a low dose. Here is an example of a typical schedule for building up to the desired level of Mysoline for an older child or adult:

    Days 1 to 3: 100 to 125 mg at bedtime
    Days 4 to 6: 100 to 125 mg each morning and evening
    Days 7 to 9: 100 to 125 mg morning, noon, and night
    Days 10 and later: 250 mg morning, noon, and night

    Patients aged 8 or older usually take one 250-mg Mysoline tablet three or four times a day to maintain control of their seizures. Some people need to take more tablets, but the total dose should not exceed 2000 mg per day.

    For children under 8 years of age, the usual dose for controlling seizures is 125 to 250 mg three times daily. The doctor may calculate the dose according to the child's weight, based on 10 to 25 mg of Mysoline per day for each kilogram (about 2.2 pounds) of the child's weight. Here is an example of a schedule that may be used to start a young child on Mysoline:

    Days 1 to 3: 50 mg at bedtime
    Days 4 to 6: 50 mg morning and evening.
    Days 7 to 9: 100 mg morning and evening
    Days 10 and later: 125 mg three times a day to 250 mg three times a day

    Be sure to use only the amount that the doctor prescribes. If you think you've taken one or two extra tablets, call your doctor for advice. For a larger overdose, call your local poison control center or emergency room right away.

    No one should stop taking Mysoline or change the amount they take without talking to the doctor first. Stopping any seizure medicine all at once can cause a serious condition called status epilepticus.

    Read the package insert of Primidone

    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 Mysoline (primidone) is found at:

    Some of the information may differ in other countries.

    To learn how to read and understand a package insert, see How to read a package insert.


    Primary Generalized Epilepsy

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