Diphenhydramine: Uses, Dosing, How to Take & Side Effects

Diphenhydramine is an antihistamine with anticholinergic, sedative and anti-tussive action. It is prescribed to relieve allergy symptoms caused by pollen, dust or other agents. Diphenhydramine can also relieve coughing, treat insomnia and manage vertigo. 

The dose and duration of treatment with diphenhydramine depends on the age of the patient and the condition being treated. Therefore, it should be used strictly as prescribed by a doctor. 

Diphenhydramine can be purchased over-the-counter at the pharmacy in syrup, pill or lotion form. It can also be administered in a hospital setting via IV or IM injection. 

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Common uses

Diphenhydramine is prescribed for: 

  • Relief of allergy symptoms, like runny nose, sneezing, itchy nose, itchy throat and eye irritation
  • Relief of skin irritation or hives, caused by plants, sun burns or insect bites 
  • Management of coughs caused by throat irritation or airway irritation 
  • Management of occasional insomnia, particularly if it is difficult to fall asleep due to nervousness or restlessness 
  • Treating motion sickness, which can cause dizziness, vertigo, nausea, vomiting, or balance issues that are triggered by movement 

Diphenhydramine can also be prescribed to control abnormal tremors or movements from medication side effects or the initial phases of Parkinson’s disease. 

How to take and dosing

The recommended diphenhydramine dose depends on the form of the medication. Guidelines are as follows: 

1. Diphenhydramine pills 

Diphenhydramine pills are available in strengths of 25 mg or 50 mg. The recommended doses are: 

  • Adults and children over 12: the general recommendation for allergy symptoms is 25 to 50 mg up to 4 times per day, for a maximum of 300 mg per day.  For insomnia,adults can take 50 mg at night, and children over 12 can take 25-50 mg, 20 to 30 minutes before going to bed. 
  • Children 6 to 12 years old: The general recommendation for allergies is 12.5 to 25 mg up to 4 times per day, depending on the pediatrician’s prescription. The maximum dose is 150 mg per day. 

For other cases, like dizziness or Parkinson’s, patients are advised to take as instructed by their doctor. 

2. Diphenhydramine syrup

Diphenhydramine syrup is available in a strength of 12.5 mg for every 5 ml (or 12.5mg/5ml). Dosing depends largely on the weight of the patient and can be used by children over 2.

  • Children between 6 and 12 years old: The recommended doses is 5 to 10 ml every 4 to 6 hours, for a maximum of 6 doses in a day. 
  • Children over 12 and adults: The recommended dose is 10 to 20 ml every 2 to 3 hours, as directed by your doctor. 

Speak to the pediatrician first before giving diphenhydramine to children between 2 and 5 years old. 

3. Diphenhydramine dissolvable tablets

The general recommended dose for chewable tablets for children is as follows: 

  • Children over 12: 2 to 4 tablets (25 to 50 mg) every 4 to 6 hours, as directed by the pediatrician. 
  • Children 6 to 11: 1 to 2 tablets (12.5 mg to 25 mg) every 4 to 6 hours, as directed by the pediatrician.

Speak to your pediatrician first before giving chewable tablets to a child between the age of 2 to 5 years old. This medication is not recommended for children under 2. 

4. Diphenhydramine lotion

Diphenhydramine lotion is usually found in combination with other active ingredients, like calamine and camphor. 

The recommended dosing for adults and children over 2 is one application over the affected region 3 to 4 times per day, for a maximum of 7 days. 

It is important to cleanse the skin with water and a mild soap and to pat dry before applying the lotion. 

Because it contains camphor, diphenhydramine lotion should not be used on children under 2, as it could be toxic. 

4. Diphenhydramine injectable 50 mg/mL

Diphenhydramine injectable solution can be applied intramuscularly (IM) or intravenously (IV) by a nurse, as prescribed by a doctor. 

Dosing for injectables are calculated by the doctor depending on the age and weight of the patient. Dosing can also vary depending on the condition being treated and the severity of doses. 

Possible side effects

The most common side effects of diphenhydramine include sedation, sleepiness, dizziness, loss of coordination, epigastric discomfort and thick bronchiole secretions. Although more rare, other side effects include dry mouth, nose or throat, chills, low blood pressure, headache, fast heart rate, nausea, loss of appetite, constipation, diarrhea, fatigue, agitation, insomnia, blurred vision and urinary retention. 

Diphenhydramine can reduce mental alertness or cause hyperactivity in children, while excessive doses can cause hallucinations, seizures or even death. 

Older adults may experience drowsiness, sedation and low blood pressure.

Contraindications for use

Diphenhydramine should not be used by people with an allergy to any of this medications’s component or by people with acute glaucoma, prostate hyperplasia, peptic ulcers, duodenal obstructions or bladder obstructions. 

This medication is also not recommended for patients who take MAO inhibitors like selegeline, moclobemide, isocarboxazid, phenylzine, nylamid, iproniazid, or trancylpromine.

There is not enough studies to prove safety during pregnancy, therefore it should only be taken as instructed by a doctor. It is not recommended for breastfeeding women, premature babies or newborns.