What is diphenhydramine?
Diphenhydramine is an antihistamine. Diphenhydramine blocks the effects of the naturally
occurring chemical histamine in the body.
Diphenhydramine is used to treat sneezing; runny nose; itching, watery eyes; hives; rashes;
itching; and other symptoms of allergies and the common cold.
Diphenhydramine is also used to suppress coughs, to treat motion sickness, to induce sleep, and
to treat mild forms of Parkinson's disease.
Diphenhydramine may also be used for purposes other than those listed in this medication guide.
What should I discuss with my healthcare provider before taking diphenhydramine?
Do not take diphenhydramine if you have taken a monoamine oxidase inhibitor (MAOI)
such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate) in the last 14 days.
A very dangerous drug interaction could occur, leading to serious side effects.
Before taking this medication, tell your doctor if you have
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glaucoma or increased pressure in the eye;
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a stomach ulcer;
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an enlarged prostate, bladder problems or difficulty
urinating;
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an overactive thyroid (hyperthyroidism);
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hypertension or any type of heart problems; or
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asthma.
You may not be able to take diphenhydramine, or you may require a lower
dose or special monitoring during treatment if you have any of the conditions listed above.
Diphenhydramine is in the FDA pregnancy category B. This means that it is not expected to
be harmful to an unborn baby. Do not take diphenhydramine without first talking to your doctor if you
are pregnant.
Infants are especially sensitive to the effects of antihistamines, and side effects could occur
in a breast-feeding baby. Do not take diphenhydramine without first talking to your doctor if you are
nursing a baby.
If you are over 60 years of age, you may be more likely to experience side effects from
diphenhydramine. You may require a lower dose of this medication.
How should I take diphenhydramine?
Take diphenhydramine exactly as directed on the package or as directed by your doctor. If you
do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.
Take each dose with a full glass of water.
Diphenhydramine can be taken with or without food.
For motion sickness, a dose is usually taken 30 minutes before motion, then with meals and at
bedtime for the duration of exposure.
As a sleep aid, diphenhydramine should be taken approximately 30 minutes before bedtime.
To ensure that you get a correct dose, measure the liquid forms of diphenhydramine with a
special dose-measuring spoon or cup, not with a regular tablespoon. If you do not have a
dose-measuring device, ask your pharmacist where you can get one.
Never take more of this medication than is prescribed for you. The maximum amount of
diphenhydramine that you should take in any 24-hour period is 300 mg.
Store diphenhydramine at room temperature away from moisture and heat.
What happens if I miss a dose of diphenhydramine?
Take the missed dose as soon as you remember. However, if it is almost time for the next dose,
skip the missed dose and take only the next regularly scheduled dose.
Do not
take a
double dose of this medication unless otherwise directed by your doctor.
Where can I get more information about diphenhydramine?
Your pharmacist has information about diphenhydramine written for health professionals that you may read.
What are the possible side effects of diphenhydramine?
Stop taking diphenhydramine and seek emergency medical attention if you experience an
allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or
hives).
Other, less serious side effects may be more likely to occur. Continue to take diphenhydramine
and talk to your doctor if you experience
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sleepiness, fatigue, or dizziness;
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headache;
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dry mouth; or
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difficulty urinating or an enlarged prostate.
This is not a complete list of side effects and others may occur. Call your
doctor for medical advice about side effects. You may report side effects to FDA at
1-800-FDA-1088. You may report side effects to FDA at 1-800-FDA-1088.
What is the most important information I should know about diphenhydramine?
Use caution when driving, operating machinery, or performing other hazardous activities.
Diphenhydramine may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid
these activities.
Use alcohol cautiously. Alcohol may increase drowsiness and dizziness while taking
diphenhydramine.
What should I avoid while taking diphenhydramine?
Use caution when driving, operating machinery, or performing other hazardous activities.
Diphenhydramine may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid
these activities.
Use alcohol cautiously. Alcohol may increase drowsiness and dizziness while taking
diphenhydramine.
What other drugs will affect diphenhydramine?
Do not take diphenhydramine if you have taken a monoamine oxidase inhibitor (MAOI)
such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate) in the last 14 days.
A very dangerous drug interaction could occur, leading to serious side effects.
Talk to your pharmacist before taking other over-the-counter cough, cold, allergy, or insomnia
medications. These products may contain medicines similar to diphenhydramine, which could lead to an
antihistamine overdose.
Before taking this medication, tell your doctor if you are taking any of the following medicines:
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anxiety or sleep medicines such as alprazolam (Xanax), diazepam
(Valium), chlordiazepoxide (Librium), temazepam (Restoril), or triazolam (Halcion);
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medications for depression such as amitriptyline (Elavil),
doxepin (Sinequan), nortriptyline (Pamelor), fluoxetine (Prozac), sertraline (Zoloft), or
paroxetine (Paxil); or
-
any other medications that make you feel drowsy, sleepy, or
relaxed.
Drugs other than those listed here may also interact with diphenhydramine.
Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines,
including vitamins, minerals, and herbal products.
What happens if I have an overdose of diphenhydramine?