Benadryl Patient Tips

Medically reviewed by Carmen Pope, BPharm. Last updated on April 7, 2025.

1. How it works

• Benadryl is used to treat allergies, motion sickness, and to help relieve symptoms of Parkinson's Disease (PD) in patients unable to tolerate more potent agents. It may also be used off-label to help induce sleep. Benadryl is a brand name for diphenhydramine.
• Diphenhydramine works in allergic-type reactions by blocking histamine-1 (H1) receptors. This prevents histamine affecting the airways, blood vessels, and the gastrointestinal tract, reversing symptoms such as bronchoconstriction (narrowing of the airways), rash and itch, and stomach cramps. Diphenhydramine also blocks acetylcholine receptors and sodium channels and inhibits the reuptake of serotonin, among other effects. These latter effects are responsible for its sleep-inducing and anti-PD actions and side effects such as a dry mouth.
• Benadryl belongs to the drug class called antihistamines. Benadryl is a first-generation antihistamine of the ethanolamine class.

2. Upsides

• Used to treat the symptoms of allergic reactions such as sneezing, itching, watery eyes, runny nose, and skin rash, and in anaphylaxis as an adjunct to epinephrine or other treatments after the acute symptoms have been controlled. Allergic reactions may be due to allergies (such as hay fever), insect bites, hay fever, allergic conjunctivitis, or urticaria (hives).
• Used to relieve nausea and vomiting associated with motion sickness.
• Also used to relieve symptoms of Parkinson's disease in seniors who are unable to tolerate more potent agents.
• May be used off-label to help people relax or fall asleep.
• Available as tablets, capsules, an oral suspension/solution, a cream, and an IV or IM injection.
• Available as an injection that may be useful when the oral form is impractical or unable to be swallowed.
• Benadryl is available as a generic under the name diphenhydramine.

3. Downsides

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:

• Drowsiness and sedation that may impair judgment and affect a person's ability to drive or operate machinery is the most common side effects reported. Alcohol should be avoided because it can make this side effect worse.
• Dizziness, low blood pressure, a headache, rapid heartbeat, disturbed coordination, abdominal discomfort, and thickening of mucus in the airways are also reported side effects. Elderly people may be more sensitive to effects such as dizziness, sedation, and low blood pressure.
• Has an atropine-like effect and may cause a dry mouth, which may increase the risk of dental caries and worsen the symptoms of gastroesophageal reflux disease (GERD) if taken regularly.
• Not suitable for use in women who are breastfeeding or for young children. Elderly people may be more susceptible to the side effects of sedation, dizziness, and low blood pressure (all of which may increase their risk of falls).
• Overdosage of Benadryl has been associated with hallucinations, convulsions, and death.
• May interact with several other drugs including benzodiazepines, antidepressants, antipsychotics, and alcohol.
• May not be suitable for some people including those with respiratory diseases such as asthma, narrow-angle glaucoma, peptic ulcer disease, intestinal obstruction, high blood pressure or heart disease, high thyroid levels, an enlarged prostate, or a narrowing of the neck of the bladder. Do not use it for people who are hypersensitive to diphenhydramine.

Note: 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. View complete list of side effects

4. Bottom Line

Benadryl is used to treat allergies, motion sickness, and to relieve symptoms of Parkinson's Disease (PD) in patients unable to tolerate more potent agents. It may also be used off-label to help induce sleep. Benadryl is a brand name for diphenhydramine. Sedation is a common side effect. Benadryl is available as tablets, capsules, an oral suspension/solution, a cream, and an IV or IM injection.

5. Tips

• Benadryl may be taken with or without food.
• Take exactly as directed. Do not take more than is recommended.
• Do not drive or operate machinery if Benadryl makes you drowsy or affects your judgment. Avoid alcohol.
• When using for motion sickness, take Benadryl 30 minutes before any exposure to motion. Take subsequent doses before meals or at bedtime for the duration of the exposure.
• Benadryl should not be used as a nighttime sleep aid in children aged less than twelve. It should not be used at all in newborn babies, especially those that have been born prematurely. In children, Benadryl can cause excitation, sedation, and overdosage may cause hallucinations, convulsions, or death.
• Ensure you maintain good oral hygiene if you are taking Benadryl long-term.
• Stand up slowly when going from a sitting or lying down position. Benadryl may cause a drop in blood pressure which may cause symptoms such as dizziness and increase your risk of falls. Remove any fall hazards in your home (such as rugs) and talk to your doctor if you are experiencing severe dizziness every time you stand up.
• Seek urgent medical advice if you experience any symptoms such as agitation, hallucinations, a fast heart rate, dizziness, flushing, muscle tremor or rigidity, nausea, vomiting, or diarrhea.
• Talk to your doctor or pharmacist before taking any other medications while you are taking Benadryl.
• Talk to your doctor before using Benadryl during pregnancy because there have been no adequate well-controlled studies on pregnant women. Do not use it while breastfeeding.

6. Response and effectiveness

• Benadryl is quickly absorbed after oral administration and peak effects are reached within one hour. The effects of diphenhydramine last from four to six hours. Benadryl in the injectable form has a rapid onset of action.
• When used as a night-time sleeping aid, the usual dosage of Benadryl is 50 mg at bedtime. A lower dosage may be needed for the elderly.

7. Interactions

Medicines that interact with Benadryl may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Benadryl. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Benadryl include:

• benzodiazepines, such as diazepam, oxazepam, and temazepam
• monoamine oxidase inhibitors, such as isocarboxazid, selegiline, or tranylcypromine
• opioids, such as oxycodone, morphine, or codeine
• sedatives, or any medication that causes sedation, such as sleeping pills, muscle relaxants, or antidepressants
• other medications that contain diphenhydramine, such as creams and gels
• other medications used to treat allergies.

Alcohol may enhance the sedative effects of Benadryl.

Note that this list is not all-inclusive and includes only common medications that may interact with Benadryl. You should refer to the prescribing information for Benadryl for a complete list of interactions.

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Frequently asked questions

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Further information

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

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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