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Viral Upper Respiratory Infections (Colds and Influenza) and Antihistamines

Read more about Antihistamines.


The main effect of antihistamines is to dry up secretions. They are also sedating, so much so that they are ingredients in all OTC sleep remedies. Second-generation antihistamines such as loratadine (Claritin) are considered non-sedating and may be available without a prescription.

Common antihistamines include:

  • Diphenhydramine
  • Chlorpheniramine
  • Brompheniramine

Effect of Antihistamines on Viral Upper Respiratory Infections (Colds and Influenza)

Antihistamines interfere in the action of substances (histamines) that cause the inflammation-related symptoms of cold and flu (such as runny nose and congestion).

Side Effects and Warnings

Possible side effects of antihistamines include:

  • Sedation
  • Drying of secretions, which impairs their clearance and may lead to complications (such as sinusitis, otitis, and pneumonia)
  • Retention or difficulty passing urine
  • Rashes
  • Dizziness
  • Headache
  • Indigestion
  • Constipation
  • Anemia

Talk to your doctor before taking these medications if you have the following conditions, which can be made worse by the side effects of antihistamines:

  • Urinary problems due to an enlarged prostate gland
  • Glaucoma
  • Breathing problems