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Phenobarbitone - What is it for

Phenobarbitone is used to control some types of seizures (commonly known as fits).

Phenobarbitone - Side Effects, Precautions, and Contraindications

What side effects can Phenobarbitone cause?

Like all medicines, this medication may cause some possible side effects but not everyone experiences them. Consult your healthcare professional if any of the side effects lasts more than a few days or become severe or bothersome.

The common side effects of Phenobarbitone include:

  • Dizziness
    • Get up slowly from sitting down or lying down position
  • Drowsiness or double vision
    • Avoid driving or engaging in activities that require concentration
  • Constipation
    • Drink more water, eat more high-fibre foods, and exercise regularly
  • Nausea, vomiting, stomach upset
    • Take the medication with or after food to reduce nausea and vomiting
    • Avoid food that is too rich, spicy or has strong smells
    • Eat small but frequent meals to reduce bloating after a meal
  • Headache
    • Take Paracetamol if needed to relieve headache
  • Difficulty sleeping, hallucinations (seeing or hearing things that are not present), vivid dreams
  • Feeling tired and restless. Some patients may experience excitement.
  • Weakened bones
    • Your doctor may prescribe calcium and vitamin D supplements for you

If the following serious side effects happen, you should consult your healthcare professional immediately:

  • Blistering, peeling, red-skin rash due to Stevens-Johnson syndrome (SJS) or Toxic Epidermal Necrolysis (TEN)
    • SJS and TEN are rare and serious skin reactions. Symptoms include face swelling, blisters on skin, skin rashes that spread within hours to days. It usually occurs within the first few months (monitor closely for the first 3 months) of treatment
    • As SJS and TEN progress rapidly, please consult your healthcare professional if you show the first sign of a rash
  • Unexplained bleeding or bruising
  • Difficulty in breathing
  • Liver problems: Dark coloured urine or light coloured stools, yellowing of your eyes or skin, severe loss of appetite, stomach pain, nausea or vomiting that does not go away

In rare cases, this medication may cause the following changes to a person's mental condition, especially in the first few weeks of treatment or during dose changes:

  • Worsening agitation, restlessness, violent behaviour
  • New or worsening thoughts of harming yourself or ending your life
  • Other changes in mood or behaviour

Please inform your doctor as soon as possible, or for your family or caregiver to inform your doctor if you are unable to seek treatment on your own.

Do not stop taking this medication on your own without discussing with your doctor.

It is important to note that your doctor has prescribed this medication as he/she feels you will benefit more from taking this medication over the possible side effects that it may cause, which have a low chance of occurring. Most people take this medication without any such problems.

The symptoms of a drug allergy include one or more of the following:

  • Swollen face/eyes/lips/tongue
  • Difficulty in breathing
  • Itchy skin rashes over your whole body

 If you experience any of these symptoms, you should stop your medication and see your healthcare professional immediately.

Before taking Phenobarbitone , what precautions must I follow?

​Inform your healthcare professional if you have the following medical conditions before starting on Phenobarbitone:

  • Liver, kidney, or heart problems
  • Severe breathing difficulties
  • Porphyria (a genetic or inherited disorder of the red blood pigment haemoglobin)
  • Anemia

For women: Tell your doctor if you are pregnant and/or breastfeeding, your doctor would have discussed the potential benefits and side effects with continuing/starting this medication but should you have further questions or concerns, do consult your doctor.

Consult your healthcare professional immediately if your seizures get worse or become different after you start on this medication.

Be careful when driving or operating machinery as this medication may cause drowsiness.

What food or medicine must I avoid when I take Phenobarbitone ?

​Avoid drinking alcohol while taking this medication as it can cause excessive drowsiness.

Phenobarbitone can decrease the effectiveness of medications that prevent pregnancy. Check with your doctor about additional or other methods of birth control.

Phenobarbitone - Dosage and How to Use

How should Phenobarbitone be used?

  • Follow the instructions on your medication label and take the medication as prescribed by your doctor.
  • If you are using oral syrup, shake the bottle well before using. Use a medicine spoon or graduated syringe provided to measure your medication. Do not use household spoons as they may not be accurate.
  • If you are taking the tablets, swallow the tablets with a glass of water. If you are unable to swallow the tablet, you may crush it and add it to a small amount of food (i.e yoghurt, ice-cream, syrup) before administering.
  • You can take this medication with or without food. You can take it with food if you experience stomach upset.
  • You should continue to take your medication regularly as instructed by your doctor even if you feel well. Stopping your medication without informing your healthcare professional may cause your condition to worsen quickly.
  • Do not stop taking or adjust the dose of this medication without consulting your healthcare professional.

What should I do if I miss a dose?

If you miss a dose, take the missed dose as soon as you remember. If it is almost time for your next dose, take only the usual dose. Do not double your dose or use extra medication to make up for the missed dose.

What should I do if I overdose?

Phenobarbitone - Handling

How should I handle Phenobarbitone safely?

Phenobarbitone - Storage

How should I store Phenobarbitone ?

;#Keep away from children;#Keep in a cool, dry place, away from direct sunlight;#

How should I dispose of Phenobarbitone safely?

​Pack this medication into a black trash bag and seal it tightly before throwing it into the rubbish chute or bin.

Phenobarbitone - Additional Information


  • Updated on 8/31/2021 12:00:00 AM
  • Article contributed by PSS National Medication Information Workgroup PSS National Medication Information Workgroup
The information provided is not intended as medical advice. Terms of use. Information provided by SingHealth

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