> Western Medicines > Diphenhydramine


Used for: Prevention or treatment of motion sickness, Allergic rhinitis, Sleep aids
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What is Diphenhydramine for?

Diphenhydramine is a first-generation antihistamine like chlorphenamine that can relieve allergic reactions such as allergic conjunctivitis, hives, angioedema, itchiness, and allergic rhinitis. Other uses of Diphenhydramine include the common cold, motion sickness, short-term management of insomnia, and Parkinsonism. Diphenhydramine is used to treat the itchiness of the skin and is an ingredient in many skin creams.

How to use it?

Diphenhydramine can be taken by mouth injection, or applied to the skin as a cream or lotion. Example dosage for different uses and age groups are as follows:


For allergic conjunctivitis due to foods / uncomplicated allergic reaction including hives or angioedema


25-50 mg 3-4 times daily


12.5-25 mg 3-4 times daily, up to a maximum of 300 mg daily OR calculate the dose based on body weight or surface area as 5mg/kg/24 hours or 150/m2/24 hours


For allergic rhinitis / common cold


Adult / Child 12 years or older
25-50 mg every 4-6 hours, up to a maximum of 300 mg daily


Child 6-12 years
12.5-25 mg every 4-6 hours, up to a maximum of 150 mg daily


For itchiness

To the skin

Adult / Child 2 years or older
Apply cream or lotion to affected area 3-4 times daily


For insomnia


Adult / Child 12 years or older
50 mg at bedtime as needed


For motion sickness


25-50 mg 3-4 times daily; For prevention, give the first dose 30 minutes before exposure to motion and similar doses before meals and upon retiring for the duration of exposure


12.5-25 mg 3-4 times daily; Max daily dosage: 300mg; Alternatively, you may also calculate dose based on body weight or surface area as 5 mg/kg/24 hours or 150/m2/24 hours; For prevention, give the first dose 30 minutes before exposure.

What are the side effects of Diphenhydramine?

Common side effects of diphenhydramine include drowsiness, dry mouth, dizziness, abnormal movement, dry mouth and nose, and thick sputum. Avoid driving or operating machinery until you know how you respond to diphenhydramine.

Who should not take Diphenhydramine?

  • People with an allergy to Diphenhydramine, other structurally related antihistamines, or any other ingredient of the drug
  • Neonates or premature infants

Pharmacist Tips:

  • Avoid taking Diphenhydramine if you are 65 years and older as you are at higher risk of side effects, such as confusion, dry mouth and constipation.
  • You should not use other products containing Diphenhydramine at the same time, even the topical ones.

Common dosing schedule:
You can take Diphenhydramine with or without food.


This schedule is for reference only, adjustments may be made according to individual needs.


Some common medications Diphenhydramine may interact:

Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Diphenhydramine in Hong Kong?

Depending on the formulation, Diphenhydramine can be classified into over-the-counter medicines and pharmacy only medicines. The oral formulations of Diphenhydramine are pharmacy only medicines and can be purchased without a prescription in a pharmacy by speaking with the pharmacist. They can also be obtained from doctors. The topical skin preparations of Diphenhydramine are over-the-counter medicines and can be purchased without a prescription from any retail outlet in Hong Kong. This includes grocery stores, convenience stores, medicine shops, and pharmacies. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.


For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at https://www.drugoffice.gov.hk

Need more information?

For detailed information about the use of Diphenhydramine in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.

Brands in Hong Kong
Available dosage
  • 25mg (Capsules)
  • 2% (Cream)
Drug class
Sub class
Antihistamines (First Generation)
Other drugs in same class
Used for: Hay fever, Asthma, Allergic rhinitis
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Used for: Motion sickness, Vertigo, Peripheral circulatory disorders
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Used for: Urticaria, Upper respiratory allergies
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