Medication Search: Phenobarbital

Learn about many of the available medications in our database.


Common Name:



How does this medication work? What will it do for me?

Phenobarbital belongs to the class of medications called barbiturates. It is used to treat insomnia (difficulty sleeping) and as a sedative to relieve the symptoms of anxiety or tension. It is also used for the control of certain types of seizures. It works by slowing down the brain and nervous system.

Phenobarbital is also used to reduce bilirubin levels in newborn babies. Bilirubin is a substance produced by the body and removed by the liver. Sometimes a newborn baby’s liver needs some time to start to work effectively.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?


Each mL of clear red liquid contains 5 mg of phenobarbital USP. Nonmedicinal ingredients: alcohol, anise oil, FD&C Red No. 2, glycerin, methyl paraben, natural and artificial flavour (lemon and orange), propyl paraben, purified water, sodium chloride, sodium cyclamate, and sucrose.


15 mg
Each white, round, biconvex tablet, debossed with ‘PH’ on one side and ’15’ on the other side contains 15 mg of phenobarbital. Nonmedicinal ingredients: gelatin, lactose monohydrate, maize starch, microcrystalline cellulose and stearic acid.

30 mg
Each white, round, biconvex tablet, debossed with ‘PH’ on one side and ’30’ on the other side contains 30 mg of phenobarbital. Nonmedicinal ingredients: gelatin, lactose monohydrate, maize starch, microcrystalline cellulose and stearic acid.

60 mg
Each white, round, biconvex tablet, debossed with ‘PH’ on one side and ’60’ on the other side contains 60 mg of phenobarbital. Nonmedicinal ingredients: gelatin, lactose monohydrate, maize starch, microcrystalline cellulose, silicon dioxide and stearic acid.

100 mg
Each white, round, biconvex tablet, debossed with ‘PH’ on one side and ‘100’ on the other side contains 100 mg of phenobarbital. Nonmedicinal ingredients: gelatin, lactose monohydrate, maize starch, microcrystalline cellulose, silicon dioxide and stearic acid.

How should I use this medication?

Adults (seizure prevention): The recommended adult dose of phenobarbital to prevent seizures ranges from 50 mg to 100 mg taken twice or three times daily. The maximum dose is 600 mg daily.

Children (seizure prevention): The recommended children’s dose ranges from 15 mg to 50 mg taken twice or three times daily.

Adults (treatment of insomnia/sedative): The recommended adult dose of phenobarbital for insomnia ranges from 100 mg to 200 mg taken at bedtime. The recommended adult dose as a sedative ranges from 30 mg to 90 mg daily in 2 or 3 divided doses.

Children (sedative): The recommended sedative dose for children is 2 mg per kilogram of body weight, taken 3 times daily.

Use an oral syringe to measure each dose of the liquid, as it gives a more accurate measurement than household teaspoons.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

This medication may be habit-forming if taken for long periods of time. You may experience withdrawal effects if you stop taking this medication suddenly after extended use. If you plan on stopping the medication, your doctor may want you to reduce the dose gradually to reduce the severity of withdrawal effects.

It is important that this medication be taken exactly as prescribed by your doctor. If you have been taking this medication on a regular basis, do not stop taking this medication without talking to your doctor first, and do not increase the dose of this medication without first talking with your doctor.

If you miss a scheduled dose, take it as soon as possible and continue on with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue on with your regular dosing schedule. Do not take a double dose of this medication. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not use phenobarbital if you:

  • are allergic to phenobarbital or any ingredients of this medication
  • have alcoholism
  • have drug dependence
  • have kidney impairment
  • have liver impairment
  • have porphyria
  • have reduced lung function
  • have severe respiratory depression
  • have sleep apnea
  • have suicidal tendencies
  • have uncontrolled pain

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • clumsiness or unsteadiness
  • constipation
  • diarrhea
  • dizziness
  • drowsiness
  • fatigue
  • feeling faint or lightheaded
  • "hangover" effect
  • headache
  • low blood pressure
  • nausea
  • nightmares or trouble sleeping
  • spinning sensation
  • trouble concentrating
  • vomiting

Although most of the side effects listed below don’t happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • abdominal pain
  • bone pain or fractures
  • confusion
  • hyperactivity in children
  • signs of anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
  • signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don’t stop bleeding)
  • signs of depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
  • signs of infection (symptoms may include fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
  • signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
  • symptoms of low sodium levels in the blood (e.g., achy, stiff or uncoordinated muscles, confusion, tiredness, weakness)
  • unusual excitement
  • vision changes (e.g., blurred vision, double vision)
  • worsening of pre-existing pain

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort
  • signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
  • thought of suicide or self-harm
  • weak or shallow breathing

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Alcohol and other medications that cause drowsiness: Do not combine this medication with alcohol or other medications that cause drowsiness (e.g., narcotic pain relievers, antidepressants, sleeping pills, anxiety medications). Doing so can cause additive drowsiness and reduced breathing, as well as other side effects, which can be dangerous and potentially fatal.

Blood counts: This medication can decrease the number of neutrophils (a type of white blood cell that helps fight infection), red blood cells (which carry oxygen), and platelets (which help your blood to clot). Your doctor will do blood tests to monitor this. If you notice any signs of infection (e.g., fever, chills, or sore throat) or unusual bleeding or bruising, contact your doctor immediately.

Bone Problems: Long term use of medications to treat epilepsy, including phenobarbital, may cause bones to become brittle, leading to decreased bone strength. If you are at risk of developing osteoporosis, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Breathing: Phenobarbital can suppress breathing. People with breathing problems, such as chronic obstructive pulmonary disease (COPD) or asthma, may be more likely to experience breathing problems. If you have breathing problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Drowsiness/reduced alertness: Barbiturates such as phenobarbital may reduce the mental and physical abilities needed for tasks such as driving a car or operating machinery. Drinking alcohol at the same time may have an additive effect. People taking this medication may be more likely to experience broken bones due to falls. This applies especially to seniors.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Skin rash: Rarely, people taking phenobarbital experience a severe skin reaction that can be life-threatening. If you experience a rash that gets worse, or develops into blisters, sores on the lips or eyes or covers a large area of the body, swollen glands, or joint swelling with or without fever, contact your doctor immediately.

Stopping the medication: If this medication needs to be stopped, it should be done gradually, under the supervision of your doctor. Suddenly stopping phenobarbital can cause a return of seizures that are difficult to control.

Suicidal or agitated behaviour: People with epilepsy sometimes experience depression. This can increase your risk of feeling agitated (restless, anxious, aggressive, emotional, and feeling not like yourself), or wanting to hurt yourself or others. If you experience these side effects or notice them in a family member who is taking this medication, contact your doctor immediately.

Withdrawal: Barbiturates such as phenobarbital may become habit-forming (physical and psychological dependence) if used for long periods of time. Withdrawal symptoms after prolonged use include:

  • insomnia
  • irritability
  • loss of appetite
  • nightmares
  • sweating
  • tremors
  • weight loss

People stopping this medication after having taken it for long periods of time should reduce the dose gradually under a doctor’s supervision.

Pregnancy: Medications used to prevent major seizures should not be stopped. The use of this medication is not recommended during pregnancy. However, the decision about whether or not to stop the medication must weigh the potential benefits against the potential risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking phenobarbital, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

What other drugs could interact with this medication?

There may be an interaction between phenobarbital and any of the following:

  • abiraterone
  • acetaminophen
  • alcohol
  • aliskiren
  • alpha agonists (e.g., clonidine, methyldopa)
  • alpha blockers (e.g., alfuzosin, doxazosin, silodosin, tamsulosin)
  • amiodarone
  • angiotensin converting enzyme inhibitors (ACEIs; captopril, ramipril)
  • angiotensin receptor blockers (ARBs; e.g., candesartan, irbesartan, losartan)
  • anti-cancer medications (e.g., brentuximab, cabazitaxel, docetaxel; doxorubicin; etoposide, ifosfamide, irinotecan, vincristine)
  • antihistamines (e.g., azelastine, bilastine, cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine, rupatadine)
  • antipsychotics (e.g., cariprazine, chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
  • apixaban
  • apomorphine
  • aprepitant
  • atorvastatin
  • "azole" antifungals (e.g., itraconazole, ketoconazole, voriconazole)
  • barbiturates (e.g., butalbital, phenobarbital)
  • benzodiazepines (e.g., alprazolam, clonazepam, diazepam, lorazepam)
  • beta-adrenergic blockers (e.g., atenolol, betaxolol, carvedilol, propranolol, sotalol)
  • birth control pills
  • brimonidine
  • bromocriptine
  • buprenorphine
  • bupropion
  • buspirone
  • butorphanol
  • calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
  • canagliflozin
  • cannabis
  • chloral hydrate
  • cholestyramine
  • clindamycin
  • cobicistat
  • conivaptan
  • oral corticosteroids (e.g., dexamethasone, hydrocortisone, prednisone)
  • cyclosporine
  • dabigatran
  • dantrolene
  • dapsone
  • darifenacin
  • deferasirox
  • desmopressin
  • dexmethylphenidate
  • diphenoxylate
  • disopyramide
  • diuretics (water pills; e.g., amiloride, furosemide, hydrochlorothiazide)
  • domperidone
  • dronedarone
  • elagolix
  • eliglustat
  • entacapone
  • enzalutamide
  • eplerenone
  • esketamine
  • estrogens (e.g., conjugated estrogen, estradiol, ethinyl estradiol)
  • everolimus
  • exemestane
  • fesoterodine
  • flibanserin
  • flunarizine
  • folic acid
  • "gliptin" diabetes medications (e.g., linagliptin, saxagliptin, sitagliptin)
  • guanfacine
  • hepatitis C antivirals (e.g., ledipasvir, letermovir, sofosbuvir, velpatasvir, voxilaprevir)
  • HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., doravirine, efavirenz, etravirine, nevirapine, rilpivirine)
  • HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
  • HIV integrase inhibitors (e.g., bictegravir, cabotegravir, dolutegravir, elvitegravir)
  • kava kava
  • ketotifen
  • isoniazid
  • ivabradine
  • ivacaftor
  • lemborexant
  • levodopa
  • lidocaine
  • macitentan
  • macrolide antibiotics (e.g., clarithromycin, erythromycin)
  • maraviroc
  • mefloquine
  • methadone
  • methotrimeprazine
  • methylphenidate
  • metoclopramide
  • metronidazole
  • mifepristone
  • mirabegron
  • mirtazapine
  • muscle relaxants (e.g., baclofen, cyclobenzaprine, methocarbamol, orphenadrine)
  • nabilone
  • naloxegol
  • narcotic pain relievers (e.g., codeine, fentanyl, morphine, oxycodone, tapentadol, tramadol)
  • nitrates (e.g., isosorbide dinitrate, isosorbide mononitrate)
  • ondansetron
  • orlistat
  • pramipexole
  • praziquantel
  • progestins (e.g., dienogest, drospirenone, levonorgestrel, medroxyprogesterone, norethindrone)
  • prasugrel
  • pregabalin
  • protein kinase inhibitors (e.g., bosutinib, dabrafenib, dasatinib, imatinib, nilotinib, vandetanib)
  • pyridoxine
  • quinidine
  • rasagiline
  • repaglinide
  • rifabutin
  • riluzole
  • riociguat
  • rivaroxaban
  • roflumilast
  • romidepsin
  • ropinirole
  • rotigotine
  • sacubitril
  • scopolamine
  • other seizure medications (e.g., carbamazepine, clobazam, levetiracetam, phenytoin, primidone, topiramate, valproic acid, zonisamide)
  • selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
  • selegiline
  • sildenafil
  • sirolimus
  • solifenacin
  • tacrolimus
  • tadalafil
  • tamoxifen
  • tenofovir
  • tetrabenazine
  • tetracyclines (e.g., doxycycline, minocycline, tetracycline)
  • theophyllines (e.g., aminophylline, oxtriphylline, theophylline)
  • thyroid replacements (e.g., dessicated thyroid, levothyroxine)
  • ticagrelor
  • tolterodine
  • tolvaptan
  • tranylcypromine
  • trazodone
  • tretinoin
  • tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
  • vitamin D analogues (e.g., calcifediol, calcitriol, cholecalciferol)
  • warfarin
  • zolpidem
  • zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

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Last Updated: 22/07/2024