Generic Name: Phenobarbital Brand Name(s): Generics only. No brands available.


What is Phenobarbital used for?

Phenobarbital is used alone or with other medications to control seizures. Controlling and reducing seizures lets you do more of your normal daily activities, reduces your risk of harm when you lose consciousness, and lessens your risk for a possibly life-threatening condition of frequent, repeated seizures. Phenobarbital belongs to a class of drugs known as barbiturate anticonvulsants/hypnotics. It works by controlling the abnormal electrical activity in the brain that occurs during a seizure. This medication is also used for a short time (usually no more than 2 weeks) to help calm you or help you sleep during periods of anxiety. It works by affecting certain parts of the brain to cause calming.

How should I take Phenobarbital?

Take this medication by mouth with or without food, usually once daily at bedtime for seizure control, or as directed by your doctor. Take with food or milk if stomach upset occurs. If you are using the liquid form of this medication, measure the dose carefully using a special measuring device/cup. Do not use a household spoon because you may not get the correct dose.

Dosage is based on your medical condition, phenobarbital blood levels, and response to treatment. The dosage in children may also be based on weight.

Your doctor may direct you to start this medication at a low dose and gradually increase your dose to prevent side effects such as drowsiness and dizziness. Follow your doctor’s instructions carefully. Do not take more or less of this drug than prescribed.

It may take several weeks to reach the best dose for you and completely control your seizures. This medication works best when the amount of drug in your body is kept at a constant level. Therefore, take it at the same time(s) each day.

Do not stop taking this medication (and other anticonvulsant medications) without consulting your doctor. Your seizures may worsen or cause a very severe seizure that is difficult to treat (status epilepticus) when this drug is suddenly stopped.

This medication may cause withdrawal reactions, especially if it has been used regularly for a long time or in high doses. In such cases, withdrawal symptoms (such as anxiety, hallucinations, twitching, trouble sleeping) may occur if you suddenly stop using this medication. Withdrawal from phenobarbital can be severe and include seizures and (rarely) death. To prevent withdrawal reactions, your doctor may reduce your dose gradually. Consult your doctor or pharmacist for more details, and report any withdrawal reactions right away.

Though it helps many people, this medication may sometimes cause addiction. This risk may be higher if you have a substance use disorder (such as overuse of or addiction to drugs/alcohol). Take this medication exactly as prescribed to lower the risk of addiction. Ask your doctor or pharmacist for more details.

When this medication is used for a long time for anxiety or to help you sleep, it may not work as well. Phenobarbital should only be used for a short time for anxiety or sleep. Talk with your doctor if this medication stops working well.

Tell your doctor if your anxiety or seizure control worsens (such as the number of seizures increases).

How do I store Phenobarbital?

Phenobarbital is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store Phenobarbital in the bathroom or the freezer. There may be different brands of Phenobarbital that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush Phenobarbital down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using Phenobarbital?

Before taking phenobarbital, tell your doctor or pharmacist if you are allergic to it; or to other barbiturates (such as primidone, secobarbital); or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: certain hormone problems (adrenal disease such as Addison’s disease), liver problems, kidney problems, lung disease (such as sleep apnea, chronic obstructive pulmonary disease-COPD), mental/mood disorders (such as depression, thoughts of suicide), personal or family history of a substance use disorder (such as overuse of or addiction to drugs/alcohol), personal/family history of a certain blood disorder (porphyria), certain vitamin deficiencies (folic acid, vitamin K).

This drug may make you dizzy or drowsy. Alcohol or marijuana can make you more dizzy or drowsy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Avoid alcoholic beverages. Talk to your doctor if you are using marijuana.

The liquid form of this product may contain alcohol or sugar. Caution is advised if you have diabetes, alcohol dependence, liver disease, or any other condition that requires you to limit/avoid these substances in your diet. Ask your doctor or pharmacist about using this product safely.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Older adults may be more sensitive to the side effects of this drug, especially drowsiness and dizziness. However, this drug can often cause excitement or confusion instead of drowsiness in older adults. Drowsiness, confusion, and dizziness can increase the risk of falling.

Children may be more sensitive to the side effects of the drug. This drug can often cause excitement instead of drowsiness in young children.

This medication is not recommended for use during pregnancy. It may harm an unborn baby. However, since untreated seizures are a serious condition that can harm both a pregnant woman and her unborn baby, do not stop taking this medication unless directed by your doctor. If you are planning pregnancy, become pregnant, or think you may be pregnant, immediately talk to your doctor about the benefits and risks of using this medication during pregnancy. Since birth control pills, patches, implants, and injections may not work if taken with this medication , discuss reliable forms of birth control with your doctor.

This medication may lower your folic acid and vitamin K levels, increasing the risk of spinal cord defects. Therefore, check with your doctor to make sure you are taking enough folic acid and vitamin K. Infants born to mothers who have been using this medication during pregnancy may also have symptoms such as fussiness, shaking, or bleeding. Tell the doctor right away if you notice any of these symptoms in your newborn.

This medication passes into breast milk and may cause excessive sleepiness or feeding problems in the nursing infant. Consult your doctor before breast-feeding.

Is it safe during pregnancy or breast-feeding?

There are no adequate studies in women for determining risk when using this Phenobarbital during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking Phenobarbital. Phenobarbital is pregnancy risk category D/B (manufacturer dependent) according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk,
  • B=No risk in some studies,
  • C=There may be some risk,
  • D=Positive evidence of risk,
  • X=Contraindicated,
  • N=Unknown

Side effects

What side effects can occur from Phenobarbital?

Dizziness, drowsiness, excitation, headache, tiredness, loss of appetite, nausea, or vomiting may occur as your body adjusts to the medication. If any of these effects persist or worsen, notify your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

A small number of people who take anticonvulsants for any condition (such as seizure, bipolar disorder, pain) may experience depression, suicidal thoughts/attempts, or other mental/mood problems. Tell your doctor right away if you or your family/caregiver notice any unusual/sudden changes in your mood, thoughts, or behavior including signs of depression, suicidal thoughts/attempts, thoughts about harming yourself.

Tell your doctor right away if you have any serious side effects, including: staggering walk/clumsiness, double vision, fast/slow/shallow breathing, fainting, slow heartbeat, severe tiredness/weakness, pale skin.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.


What drugs may interact with Phenobarbital?

Some products that may interact with this drug include: darunavir, etravirine, orlistat, rilpivirine.

Other medications can affect the removal of phenobarbital from your body, which may affect how phenobarbital works. Examples include St. John’s wort, among others.

This medication can speed up the removal of other medications from your body, which may affect how they work. Examples of affected drugs include artemether/lumefantrine, asunaprevir, atazanavir, boceprevir, cobicistat, lurasidone, ranolazine, sofosbuvir, sorafenib, voriconazole, certain calcium channel blockers such as felodipine/nimodipine, among others.

This medication may decrease the effectiveness of hormonal birth control such as pills, patch, or ring. This could cause pregnancy. Discuss with your doctor or pharmacist if you should use reliable backup birth control methods while using this medication. Also tell your doctor if you have any new spotting or breakthrough bleeding, because these may be signs that your birth control is not working well.

The risk of serious side effects (such as slow/shallow breathing, severe drowsiness/dizziness) may be increased if this medication is taken with other products that may also cause drowsiness or breathing problems. Tell your doctor or pharmacist if you are taking other products such as opioid pain or cough relievers (such as codeine, hydrocodone), alcohol, marijuana, other drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), muscle relaxants (such as carisoprodol, cyclobenzaprine), or antihistamines (such as cetirizine, diphenhydramine).

Check the labels on all your medicines (such as allergy or cough-and-cold products) because they may contain ingredients that cause drowsiness. Ask your pharmacist about using those products safely.

Phenobarbital is very similar to primidone. Do not use medications containing primidone while using phenobarbital.

Phenobarbital may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Does food or alcohol interact with Phenobarbital?

Phenobarbital may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with Phenobarbital?

Phenobarbital may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.


The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using this Phenobarbital.

What is the dose of Phenobarbital for an adult?

Usual Adult Dose for Sedation

Daytime Sedation:

30 to 120 mg orally, IM, or IV in 2 or 3 divided doses

Maximum dose: 400 mg during a 24-hour period

Preoperative Sedation:


100 to 200 mg IM 60 to 90 minutes before surgery


-Frequency of administration should be determined by the patient response.

-Parenteral administration should be reserved for situations in which oral administration is impossible/impractical.

Uses: Daytime sedation; preoperative sedation

Usual Adult Dose for Insomnia


-Recommended dose: 100 to 200 mg orally once a day

-Maximum dose: 400 mg during a 24-hour period


-Recommended dose: 100 to 320 mg IM or IV once a day

-Maximum dose: 400 mg during a 24-hour period


-This drug may begin to lose effectiveness for inducing and maintaining sleep after 2 weeks.

Uses: Bedtime hypnosis; hypnosis

Usual Adult Dose for Seizures

Acute Convulsions


20 to 320 mg IM or IV every 6 hours as necessary



60 to 200 mg orally per day


-Maintenance doses should be determined by clinical laboratory reference values.

-Prevention of febrile seizures may not influence the development of epilepsy.

Uses: Treatment of generalized and partial seizures; treatment/prophylaxis of febrile seizures

Renal Dose Adjustments

Dose adjustments may be required; however, no specific guidelines have been suggested. Caution recommended.

Liver Dose Adjustments

Mild to moderate liver impairment: Dose adjustments may be required; however, no specific guidelines have been suggested. Caution recommended.

Marked/severe liver impairment: Contraindicated

Dose Adjustments

-Geriatric or debilitated patients: This drug should be used at a reduced dosage due to an increased risk of sensitivity; however, no specific dose adjustment guidelines have been suggested.

-Clinical laboratory reference values should be used to determine the therapeutic anticonvulsant level of phenobarbital in serum.

-To achieve the blood levels considered therapeutic in children, higher per kg doses are generally necessary.

Therapeutic drug range: 5 to 40 mcg/mL (sedation)



-This drug should be considered a narrow therapeutic index (NTI) drug as small differences in dose or blood concentrations may lead to serious therapeutic failures or adverse drug reactions.


– Generic substitution should be done cautiously, if at all, as current bioequivalence standards are generally insufficient for NTI drugs.

-Additional and/or more frequent monitoring should be done to ensure receipt of an effective dose while avoiding unnecessary toxicities.

Other Comments

Administration advice:

-The IV formulation should be diluted prior to use and the infusion rate should not exceed 60 mg/min in adults.

-If given IM, limit the volume to 5 mL per site. Injections should be administered deeply into large muscles.

Storage requirements:

-The manufacturer product information should be consulted.

Reconstitution/preparation techniques:

-The manufacturer product information should be consulted.


-If discontinuation is necessary, this drug should be withdrawn slowly to prevent seizures or status epilepticus.

-Dosing should be based on a patient’s age, weight, and condition.

-Anticonvulsant activity is believed to be present at sub-hypnotic doses.


-Blood pressure, respiration, and cardiac function during IV administration or IM (at hypnotic doses).

-Hematopoietic, renal and hepatic function periodically, especially during long-term therapy.

-Bone mineral density, especially during prolonged treatment.

Patient advice:

-Advise patients, and families/caregivers to monitor and report signs/symptoms of suicidality, and/or unusual behavior immediately to their healthcare provider (e.g., agitation, irritability, anxiety, panic attacks, insomnia, hostility, aggressiveness, impulsivity, akathisia, hypomania/mania).

-Patients should be cautioned about performing activities requiring mental alertness, such as operating hazardous machinery or a motor vehicle, until they are reasonably certain that this drug does not adversely affect them.

-Patients should be told to avoid consuming alcohol while taking this drug.

-Instruct patients to immediately report any signs/symptoms of Stevens-Johnson syndrome, toxic epidermal necrolysis, hematological disease, or hypersensitivity reactions.

-Patients should be advised to report all concurrent prescription and nonprescription medications or herbal products they are taking.

-Advise patients to speak to their healthcare provider if they become pregnant, intend to become pregnant, or are breastfeeding.

What is the dose of Phenobarbital for a child?

Usual Pediatric Dose for Seizures



-Initial dose: 15 to 20 mg/kg orally

-Recommended dose: 3 to 6 mg/kg orally


4 to 6 mg/kg/day for 7 to 10 days or 5 to 15 mg/kg/day IM or IV

Status epilepticus:


-Initial dose: 15 to 20 mg/kg IV over 10 to 15 minutes


-Loading doses of 15 to 20 mg/kg are predicted to produce blood levels of approximately 20 mcg/mL after administration.

-Maintenance doses should be determined by clinical laboratory reference values.

-Prevention of febrile seizures may not influence the development of epilepsy.

Uses: Anticonvulsant used for the treatment of generalized and partial seizures, treatment/prophylaxis of febrile seizures, and treatment of status epilepticus.

Usual Pediatric Dose for Sedation


1 to 3 mg/kg IM or IV

Use: Preoperative sedation

How is Phenobarbital available?

Phenobarbital is available in the following dosage forms and strengths:

  • Oral tablet,
  • Oral elixir,
  • Injectable solution,
  • Oral capsule,
  • Compounding powder.

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of Phenobarbital, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Review Date: April 11, 2018 | Last Modified: April 11, 2018

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