Naomi Carr
Author: Naomi Carr Medical Reviewer: Dr. Brittany Ferri, PhD Last updated:

Primidone, commonly known as Mysoline, is a barbiturate anticonvulsant medication, primarily used to treat epileptic seizures. It is important to take this medication exactly as prescribed and consult with your doctor before starting any other medication (prescribed or over the counter) while on primidone, as adverse effects can occur.

Primidone brand names

  • Mysoline

What is primidone prescribed for?

Primidone is primarily prescribed as an antiepileptic medication, to treat certain types of epileptic seizure. It is also prescribed to treat essential tremors, an involuntary muscle movement disorder [1].

Often, anticonvulsant drugs are prescribed to treat bipolar disorder, as a mood stabilizer. Primidone can be prescribed for this use, although it has been found to have limited success when compared to other mood stabilizers, such as carbamazepine and valproate [2][3].

How does primidone work?

Primidone works by impacting sodium and calcium channels in the brain, reducing certain nerve activity, which reduces the occurrence of seizures and tremors [4][5].

It also impacts the function of ion channels and neurotransmitters, which has effects on mood and behavior, acting as a mood stabilizer. However, these effects differ from person to person [3].

How is primidone usually taken?

Primidone is available in 50mg and 250mg tablets, which should be swallowed whole without crushing.

If you are prescribed primidone, your doctor will likely start your treatment with a low dose and gradually increase the dosage every three days [6].

For adults, the initial dosage will be 100mg per day, which can then be increased up to 1g per day, divided into 3-4 doses. The dose can be increased up to an absolute maximum of 2g per day – divided into doses of 500 mg taken 4 times daily – but the daily dosage should not exceed this amount.

For children, the initial dose will be 50mg per day, which can be increased up to 750mg per day, divided into 3-4 doses. The maximum daily dose for children will be dependent on weight [7].

Your doctor will closely monitor your physical health, particularly at the start of your treatment, which will likely include regular blood tests.

This medication should be taken exactly as prescribed, without missing a dose. If a dose is missed, take the medication as soon as possible, or if it is close to the next dosage time, skip the missed dose. Never take double your prescribed dose in one go, as this can have adverse effects and may increase the risk of side effects.

How long does primidone stay in your system?

When you start taking primidone, it may take several weeks for the medication to take full effect, so it is important to continue taking it exactly as prescribed, in order to reach a therapeutic level.

After you stop taking primidone, the effects of the medication can wear off within a day or two, but it may take several weeks for the medication to entirely leave your system [4].

Do not suddenly stop taking primidone, even if you feel better, as this can have serious impacts on your physical and mental health and can cause a reoccurrence of seizures. If your doctor advises that it is safe to come off this medication, they will likely reduce your prescription slowly, to prevent adverse effects.

Primidone side effects

When you begin a new medication, you may experience some common side effects. They will likely reduce within the first week or two, but if they continue or become problematic, seek medical advice immediately, as you may need a reduced dose or a change of medication.

Common side effects of primidone include:

  • Drowsiness
  • Loss of appetite
  • Nausea and vomiting
  • Feeling dizzy and unsteady
  • Blurry vision

Severe side effects of primidone are less common but may still occur. Contact your doctor immediately if you experience any of the following:

  • Fever
  • Sore throat
  • Swollen glands
  • Signs of infection
  • Breathing difficulties
  • Allergic reaction, including rash, hives, sores, or blisters
  • Changes in mental state, including emerging or worsening depression or anxiety, insomnia, agitation, aggression, or suicidal thoughts

Primidone precautions

Primidone can cause suicidal thoughts, particularly at the beginning of your treatment [7]. If you or your family notice any concerning changes in your mental state, or you experience thoughts of harming yourself, contact a medical professional immediately.

It is important that your doctor is aware of any past or present mental health conditions you have experienced, to enable safe monitoring of your condition while on this medication, or to decide if it is safe for you.

Discuss with your doctor all your past and present physical health conditions, as they may impact your ability to take this medication safely.

If you have ever been diagnosed with porphyria, it may not be safe to take primidone [7].

Ensure you inform your doctor if you have had liver or kidney problems, as it may not be safe for you to take primidone, or your doctor may wish to prescribe a lower dose and closely monitor your physical health.

Tell your doctor about all medications you are currently taking, or plan to take (including vitamins and dietary supplements), as they may cause adverse reactions.

Ensure you tell your doctor if you are pregnant or planning to become pregnant while taking primidone, as it may cause harm to the fetus. As such, it is advised to only start or continue primidone treatment while pregnant if the benefits of treatment outweigh the potential risks, and careful monitoring will be required.

Tell your doctor if you are breastfeeding, as primidone can be passed to your baby through breast milk, so it should be used with caution, along with closely monitoring your baby for any unusual changes in their mental or physical state. Alternative treatment may be available, or you may wish to stop breastfeeding if primidone is deemed necessary for treatment.

This medication can cause drowsiness and sedation, so it is important to avoid driving until you are aware of how primidone affects you and it is safe to do so.

Primidone interactions

Some medications may interact with primidone, causing a decrease in the effectiveness of your medication, or an increase in the risk of side effects. This includes blood thinners, other seizure medications, antibiotics, steroids, disulfiram, pain medications, mental health medications, including antidepressants and anti-anxiety medications, sedatives, tranquilizers, and sleeping pills [6].

Always discuss your medications with your doctor before starting a new treatment.

It is advised to avoid or limit alcohol intake while on primidone, as alcohol can increase drowsiness and sedation, increasing the risk of falls and accidents.

Primidone storage

Always keep all medications out of reach of children.

Store primidone in its original packaging, in airtight containers, and at room temperature (68°F to 77°F).

If you need to dispose of medication that is out of date or no longer needed, contact a medical professional to ensure it is disposed of appropriately. Never flush medications down the toilet or put them in the bin, as this can create unnecessary risks.

What to do if you overdose on primidone

If you overdose on primidone, call a medical professional, or the Poison Control Center on 1-800-222-1222. In case of an emergency, call 911 and seek urgent medical attention. Symptoms of a primidone overdose include slowed breathing, slowed or irregular heartbeat, slowed speech, and coma.

Frequently asked questions about primidone

Is primidone a sedative?

Primidone regularly causes a side effect of sedation and drowsiness, which is why it is often prescribed to be taken in the evening, to reduce daytime sedation [1].

It is not prescribed as a sedative but may help in falling asleep because of its sedating effects. However, it has been found to reduce the amount of REM sleep, so is considered detrimental to good sleep [8].

Sedation may be an undesirable side effect for many, as it can cause excessive daytime sleepiness, so other anticonvulsant drugs may be preferred, that cause less sedation.

How effective is primidone for tremors?

Primidone has been found to be very effective in the treatment of essential tremors, at doses between 50mg and 1000mg per day. It can reduce the severity of tremors within 1-7 hours of dosage administration and is considered equally, or more, effective for this use than propranolol [9][10].

  1. Lenkapothula, N., & Cascella, M. (2022). Primidone. In StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing. Retrieved from
  2. Schaffer, L.C., Schaffer, C.B., & Caretto, J. (1999). The Use of Primidone in the Treatment of Refractory Bipolar Disorder. Annals of Clinical Psychiatry: Official Journal of the American Academy of Clinical Psychiatrists, 11(2), 61–66. Retrieved from
  3. Nadkarni, S., & Devinsky, O. (2005). Psychotropic Effects of Antiepileptic Drugs. Epilepsy Currents, 5(5), 176–181. Retrieved from
  4. National Center for Biotechnology Information (2022). PubChem Compound Summary for CID 4909, Primidone. Retrieved from
  5. National Library of Medicine. (2012). Primidone. In LiverTox: Clinical and Research Information on Drug-Induced Liver Injury [Internet]. Bethesda, MD: National Institute of Diabetes and Digestive and Kidney Diseases. Retrieved from
  6. American Society of Health-System Pharmacists, Inc. (Revised 2020). Primidone. MedlinePlus. Retrieved from
  7. Bausch Health Companies Inc. (Revised 2020). Mysoline. Access Data FDA. Retrieved from
  8. Epilepsy Foundation. (Reviewed 2014). Sleep and Seizure Medication. Epilepsy Foundation. Retrieved from
  9. National Institute of Neurological Disorders and Stroke. (Reviewed 2022). Essential Tremor. NIH. Retrieved from
  10. Koller, W.C., & Royse, V.L. (1986). Efficacy of Primidone in Essential Tremor. Neurology, 36(1), 121–124. Retrieved from
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Naomi Carr
Author Naomi Carr Writer

Naomi Carr is a writer with a background in English Literature from Oxford Brookes University.

Published: Dec 22nd 2022, Last edited: Oct 27th 2023

Brittany Ferri
Medical Reviewer Dr. Brittany Ferri, PhD OTR/L

Dr. Brittany Ferri, PhD, is a medical reviewer and subject matter expert in behavioral health, pediatrics, and telehealth.

Content reviewed by a medical professional. Last reviewed: Dec 22nd 2022