Phenobarbital

generic

Phenobarbital Side Effects

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.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.
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  • megaloblastic anemia
  • thrombocytopenic disorder
  • agranulocytosis
  • acute confusion
  • excitement
  • psychiatric disorder
  • drug dependence
  • nightmares
  • agitation
  • depression
  • hyperkinesis
  • bradycardia
  • hypotension
  • throat constriction
  • constipation
  • drug-induced hepatitis
  • allergic dermatitis
  • Stevens-Johnson syndrome
  • exfoliative dermatitis
  • urticaria
  • osteopenia
  • altered consciousness
  • drowsy
  • memory impairment
  • hallucinations
  • syncope
  • vertigo
  • dizziness
  • insomnia
  • ataxia
  • skin rash
  • headache disorder
  • apnea
  • wheezing
  • dyspnea
  • nausea
  • vomiting
  • CNS depression
  • nervousness
  • anaphylaxis
  • angioedema
  • hypersensitivity drug reaction
  • lethargy
  • hypoventilation
  • irritability
  • accidental fall
  • complex sleep behavior
  • symptoms of anxiety
  • disturbance in thinking

Drug Interactions

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

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 (cannabis), 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.