Medication Information Leaflet

What is this medication for?

How should I take or use this medication?

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 forget to take or use this medication?

What precautions should I take when taking or using this medication?

What are some common side effects of this medication?

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 and bothersome.

The common side effects of Phenobarbitone include:

• Dizziness
  • Stand up or sit up slowly from a lying or sitting position.
• Drowsiness or double vision
  • This may affect your ability to drive and use machinery.
  • Make sure your reactions are normal before you drive or do things that require you to be alert. 
• Difficulty in passing stools (Constipation)
  • You should have more vegetables and fruits in your diet (at least 2 servings of vegetables and fruits daily) and drink enough water (at least 2 litres or 8 glasses of water daily). 
  • If your constipation does not get better with self-treatment, you should see your doctor.
• Nausea, vomiting, stomach upset
  • Take the medication after food, eat small but frequent meals. 
  • Avoid fatty or spicy food.
• Headache
  • You may take paracetamol to treat the 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

What are some rare but serious side-effects that I need to seek medical advice immediately?

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.

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 which can happen after using some medications. 
  • Symptoms include mouth ulcers, face swelling, blisters on skin, skin rashes that spread throughout the body within hours to days after starting the medication. 
  • This usually occurs within the first few months (monitor closely for the first 3 months) of treatment.
• Unexplained bleeding or bruising
• Difficulty in breathing
• Symptoms of liver problems include:
  • Yellowing of your skin and whites of the eyes
  • Dark coloured urine or light-coloured stools
  • Nausea and vomiting that does not go away 
  • Loss of appetite
  • Stomach pain

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.

What food or medication should I avoid when I take or use this medication?

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

Avoid use with opioids as it can cause excessive drowsiness and respiratory depression. 

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

How should I store this medication?

How do I throw away this medication safely?

Disclaimer

Please take note that the above is not a complete list of all possible side effects. If you have any concerns about your medication or if you have other side effects that you think are caused by this medication, please consult your doctor or pharmacist.

If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last updated on Jan 2025