Antihistamine (Oral)

Information on oral Antihistamines including Antihistamine uses and side effects.

What are Antihistamines used for?

Antihistamines are a group of medications which can be used for the following conditions:

  • Relief of sneezing
  • Relief of watery eyes
  • Relief of runny nose (due to a cold, flu or allergies)
  • Relief of itch in the eyes, nose or skin (due to an insect bite or allergies)
  • Relief of redness and swelling of the skin and eyes 
  • Prevention and relief of nausea
  • Relief of cough

Some Antihistamines, such as Chlorpheniramine, Dexchlorpheniramine, Tripolidine, Diphenhydramine, Hydroxyzine and Promethazine may cause drowsiness.

Other newer Antihistamines, such as Cetirizine, Loratadine, Fexofenadine, Desloratidine and Levocetirizine are less likely to cause drowsiness

While some Antihistamines may be available over-the-counter, other Antihistamines require a doctor’s prescription. 

How should I take/use Antihistamines?

  • Take Antihistamines when necessary to relieve your symptoms
  • Different Antihistamines have different maximum doses, do not exceed the maximum dose as recommended by your healthcare professional.
  • You may take Antihistamines with or without food. However, food may slow down the absorption of Antihistamines leading to a slower time to take effect.

What should I do if I forget to take/use Antihistamines?

If you forget to take a dose, take it as soon as you remember. Then take your next dose at the usual time. Do not take two doses to make up for the missed dose.

When Taking Antihistamines, what precautions should I take?

Inform your healthcare professional if:

  • You are allergic to Antihistamines or any of the other ingredients of this medication
  • You are pregnant, planning to become pregnant, or breastfeeding
  • You are taking any other medications, including supplements, traditional medications and herbal remedies.
  • You have difficulty urinating or have a history of other bladder conditions

What are some common Antihistamine side effects?

  • Some Antihistamines may cause drowsiness or dizziness
    • Avoid driving, operating machinery or other activities which require concentration while on this medication
  • Dry mouth, skin and eyes
    • Drink more water or suck an ice cube to help with mouth dryness
    • Use moisturising eye drops to resolve eye dryness
  • Difficulty in passing urine 
    • Stop taking Antihistamines and consult your healthcare professional for other alternatives
  • Confusion in the elderly or very young children
    • Stop taking Antihistamines and consult your healthcare professional for other alternatives

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

The symptoms of a drug allergy to Antihistamines 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 taking Antihistamines and see your healthcare professional immediately.

If you continue to experience symptoms for more than 2 weeks even with self-treatment or have any of the following symptoms:

  • Blood in your phlegm or mucous
  • Unexplained weight loss, constant fatigue, night sweats

Your condition may be too serious for self-treatment and you should consult a doctor

What food or medication should I avoid when I take Antihistamines?

If you are taking a type of medication known as monoamine oxidase inhibitors (e.g. Rasagiline), contact your healthcare professional before taking Antihistamines containing chlorpheniramine or brompheniramine as your blood pressure may drop dangerously low

Taking Antihistamines with alcohol may worsen the drowsy side effect. Avoid all alcohol while on Antihistamines.

Many over-the-counter medications contain Antihistamines, always check with your health care professional before taking two over-the-counter medications at the same time to prevent overdosing.

How should I store Antihistamines?

Store in a cool and dry place, away from direct sunlight. Keep Antihistamines away from children.

How should I throw away Antihistamines safely?

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

Disclaimers

If you take more than the recommended Antihistamine dosage, 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.

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Antihistamine (Oral)

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