Diphenhydramine is a common ingredient that is used in a variety of over-the-counter (OTC) medications that can be used in a variety of forms, including single-ingredient and combination-ingredient products, and as pills, capsules, liquids, and chewable tablets. The most common brand name is Benadryl.
Uses
Diphenhydramine is most commonly used to treat allergic symptoms caused by histamine release. It is also used for the following purposes:
Anaphylaxis Insomnia Antitussive (anti-cough) Parkinsonian syndrome including extrapyramidal symptoms Prevention and treatment of motion sickness Cold symptoms
Off-Label Uses
These are uses that are not indicated for medication by the Food and Drug Administration (FDA), but a healthcare provider may recommend using it nonetheless:
Angioedema Infusion or transfusion-related reactions Nausea and vomiting Scombroid (histamine) poisoning Urticaria (hives) Acute vertigo
Before Taking
Your medical provider will determine your medication dose and timing. It is important to note that diphenhydramine is an OTC medication, and safe dosing instructions are found on all generic and brands of this medication.
How to take diphenhydramine:
Inform all of your healthcare providers that you are taking this drug. Tell your healthcare provider about all other medications, vitamins, and supplements that you are taking, as some may interact with diphenhydramine. Diphenhydramine can be taken via tablet, liquid, and/or intravenously. Chewable tablets and oral-disintegrating tablets should be chewed well or dissolved completely in the mouth. Diphenhydramine can be taken with or without food. Diphenhydramine is taken as needed, but do not take more than the maximum recommended dose. Take the medication dosage as ordered by your medical provider or as indicated on the packaging. Avoid driving or operating heavy machinery until you are aware of how the medication will affect you. Don’t use alcohol when you have diphenhydramine in your system. Talk with your healthcare provider if you are planning to use marijuana. Do not take if you are pregnant or breastfeeding unless directed to do so by your healthcare provider. Do not take other medications containing diphenhydramine.
Other Antihistamines
Diphenhydramine is one of the first-generation antihistamines, which are known to be sedating. Others include brompheniramine, chlorpheniramine, dimenhydrinate, and doxylamine.
Second-generation antihistamines are non-sedating. These include Alavert and Claritin (loratadine), Zyrtec (cetirizine), and Allegra (fexofenadine).
Dosage
All listed dosages are according to the drug manufacturer. Check your prescription and talk to your healthcare provider to make sure you are taking the right dose for you.
General Adult Dosage Information
These dosages are suggested by the manufacturer:
Extrapyramidal reaction: 25 to 50 milligrams (mg) orally 3 to 4 times a dayInsomnia: 50 mg orally once a day at bedtimeMotion sickness: 25 to 50 mg 3 to 4 times a dayAllergic rhinitis: 25 to 50 mg orally every 4 to 6 hours as needed Maximum dose: 300 mg/dayCold symptoms: 25 to 50 mg orally every 4 to 6 hours as needed. Maximum dose: 300 mg/dayPruritus: 25 to 50 mg orally every 4 to 6 hours as needed. Maximum dose: 300 mg/dayUrticaria: 25 to 50 mg orally every 4 to 6 hours as needed. Maximum dose: 300 mg/day
Pediatric Dosage Information
There are many formulations of products that contain diphenhydramine for children, but it is important to note the age restrictions and recommended dosages. These are examples.
Store at room temperature and protected from light. Store in a dry place. Do not refrigerate or freeze. Throw away liquid suspension after eight weeks due to potential instability. Throw away unused or expired medication.
Side Effects
Most side effects associated with this medication are not harmful, but you should tell your healthcare provider about all of your side effects.
Common side effects can include:
Sedation/sleepiness Dizziness Epigastric distress (abdominal discomfort) Thickening of secretions Headache Coordination difficulties Dry mouth Vertigo Urticaria Irritability Euphoria
Serious side effects, which should be immediately reported to your healthcare provider, include:
Tremor Convulsions Blurred vision Anaphylactic shock Chest tightness Palpitations (sense of a rapid or throbbing heartbeat) Hallucinations Extrapyramidal effects (tremors, stiffness, spasms, and/or involuntary movements) Pharyngeal edema (severe swelling and tightness in your throat)
Hemolytic anemia and thrombocytopenia are side effects that involve blood cells. Symptoms can include fatigue, weakness, rapid pulse, shortness of breath, bleeding, and/or bruising,
Warnings and Interactions
Diphenhydramine or any medications containing it should not be used by adults age 65 or older unless directed by a healthcare provider.
Diphenhydramine should be used with caution by people to whom any of the following may apply, so check with your healthcare provider before using:
Breastfeeding History of hypotension A history of alcoholism or drug abuse Are currently taking benzodiazepines, antidepressants, and/or antipsychotics Have a history of asthma Have a history of narrow-angle glaucoma Have a history of peptic ulcer disease Have an intestinal obstruction Have a history of high blood pressure or heart disease
A Word From Verywell
Children and the elderly are more sensitive to the effects of antihistamine, and special precautions should be taken when using these products in these age groups. Antihistamines such as Benadryl or others should never be given to children under 4 years of age. These medications can cause life-threatening side effects. Always read and follow the directions on the labels and consult with your healthcare providers or pharmacists if you have concerns or questions.
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