Antihistamines (Oral)
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Patient Guide

 Antihistamines (Oral)

 Antihistamines (Oral)

About your medicine

Your doctor has prescribed one or more of the following antihistamine(s):

Drowsy Non-drowsy
  • Buclizine
  • Chlorpheniramine
  • Hydroxyzine
  • Promethazine
  • Bilastine
  • Cetirizine (may cause mild sedation)
  • Desloratadine
  • Fexofenadine
  • Levocetirizine
  • Loratadine
  • Rupatadin​e

What are antihistamines used for?

Antihistamines are used to relieve itch, redness and swelling in some skin conditions and other types of allergy. They also help to relieve some of the symptoms of the common flu and hay fever, like sneezing, runny nose and watery eyes.

They work by canceling the effects of histamine produced by the body in allergic conditions.

How should you take antihistamines?

  • Antihistamines are available in tablets or liquids. Follow the dosage instructions on the label. Do not take more than recommended unless advised by your doctor.
  • Take this medicine with some food to reduce stomach irritation if necessary.
  • ​For patients taking bilastine:
    Take bilastine one hour before or 2 hours after intake of food or fruit juice.

What should you do if you forget a dose?

  • Take the missed dose as soon as you remember. If it is almost time for your next dose, do not take the missed dose at all. Resume your regular dosing schedule. Do not take double the dose to make up for the missed one.

What other effects may antihistamines cause?

Certain side effects of this medicine are not unusual and may even disappear during treatment. If any of the following effects persist or are severe, consult your doctor:

  • Some antihistamines may cause some people to feel drowsy, while other antihistamines do not have this effect at all. If you are affected, do not drive, operate machinery or do work that requires you to be alert.
  • Blurred vision
  • Difficult or painful urination
  • Dry mouth (drink fluids or suck sweets to relieve this)
  • GI upset (bloating, constipation or diarrhoea)

What precautions should you take?

  • For women: Tell your doctor if you are pregnant, plan to become pregnant or are breast-feeding.
  • Inform your doctor if you regularly use other medicines that make you sleepy (such as cold or allergy medicine, sedatives, narcotic pain medicine, sleeping pills, muscle relaxants, and medicine for seizures, depression, or anxiety). They can add to sleepiness caused by antihistamines.
  • Avoid drinking alcohol. Alcohol may increase drowsiness or dizziness while taking antihistamines.
  • Inform your doctor that you are taking antihistamines before you have any skin tests for allergies. The results of the test may be affected by antihistamines.
  • Inform your doctor if you are taking over-the-counter medicines, including vitamins, minerals, and herbal products.

How should you store antihistamines?

  • Store this medicine away from heat and direct sunlight in a cool, dry place, out of reach of children
  • Do not keep this medicine with other medications in the same container. Keep medicines separately in labeled containers.

When in doubt, consult your doctor or pharmacist.
National Skin Centre (Singapore)
1 Mandalay Road, Singapore 308205
Tel: 63508454


Last updated on 30 Apr 2020

Last updated on 30 Apr 2020