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Diphenhydramine Patient Tips

Written by C. Fookes, BPharm on Feb 24, 2016

How it works

Diphenhydramine is an antihistamine that works on histamine receptors to block the allergic response.


  • Used to treat allergic-type reactions including allergic conjunctivitis, urticaria (hives), and in addition to epinephrine for anaphylactic reactions.
  • Also effective at relieving motion sickness.
  • Good for controlling symptoms such as sneezing, itching, watery eyes, and runny nose.
  • May also be used for elderly people with Parkinson's disease unable to tolerate more potent agents.
  • Can be used as a night-time sleep aid.


If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • May cause drowsiness and sedation and impair judgement and affect ability to drive or operate machinery. Avoid alcohol.
  • Other reasonably common side effects include dizziness, low blood pressure, a dry mouth, headache, rapid heart beat, disturbed coordination, abdominal symptoms and a thickening of bronchial secretions.

Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.

Bottom Line

Diphenhydramine is an antihistamine that can be used to treat allergic reactions, relieve motion sickness, and as a sleep aid; however, it is likely to cause drowsiness.


  • Do not drive or operate machinery if diphenhydramine makes you drowsy or affects your judgement. Avoid alcohol.
  • When using for motion sickness, take diphenhydramine 30 minutes before exposure to motion. Take subsequent doses before meals or bed-time for duration of the exposure.
  • Not recommended as a night-time sleep aid for children aged less than twelve.

Response and Effectiveness

Diphenhydramine is quickly absorbed with maximum activity occurring within one hour. Effects of diphenhydramine last from four to six hours.


Diphenhydramine [package insert]. Revised 07/2012. Pharmaceutical Associates, Inc. Accessed 02/2016

  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use diphenhydramine only for the indication prescribed.

  • Disclaimer: Every effort has been made to ensure that this information is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. This drug information does not endorse drugs, diagnose patients or recommend therapy. It is an informational resource designed as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of this information. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2017 Revision Date: 2016-02-24 00:00:00