Cold Home > Diphenhydramine Adverse Reactions

Diphenhydramine (Benadryl®, Sominex®, and many other brand names) is an antihistamine medication that is available both over the counter and by prescription. It is used for treating a variety of conditions, including allergies and insomnia.
As with any medication, side effects are possible with diphenhydramine. Adverse reactions may include:
  • Sedation (a feeling of sleepiness and reduced anxiety)
  • Drowsiness
  • Dizziness
  • Coordination problems
  • Indigestion or heartburn
  • Thickening of bronchial secretions (chest mucus).
In most cases, side effects of diphenhydramine are minor and either do not require medical attention or can be treated easily by you or your healthcare provider. However, certain side effects are potentially serious and should be reported to your healthcare provider right away. Seek medical attention immediately if you experience:
  • Low blood pressure (hypotension)
  • Heart palpitations
  • A rapid heart rate (tachycardia)
  • An irregular heartbeat
  • Anemia
  • Low blood platelets
  • Confusion
  • Blurred vision or double vision
  • Loss of balance, especially if accompanied by ringing of the ears (tinnitus) or hearing loss
  • Seizures
  • Difficulty passing urine
  • Hallucinations or delirium.
(Click Diphenhydramine Side Effects to learn about other possible adverse reactions and for a more complete list of potentially serious side effects that require immediate medical attention.)
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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