Some older patients with Parkinson's disease (a type of brain disorder that leads to serious difficulties
with muscle movements), who cannot take stronger drugs for this condition, take diphenhydramine
hydrochloride because it decreases muscle stiffness and tremors (uncontrollable shaking movements).
Some younger patients with mild Parkinson's disease also take diphenhydramine hydrochloride. Because
it helps control involuntary muscle movements, diphenhydramine hydrochloride is also given to patients
who have developed involuntary movements as a side effect from another drug.
WHAT FORMS ARE DIPHENHYDRAMINE HYDROCHLORIDE AVAILABLE IN AND HOW SHOULD IT
Diphenhydramine hydrochloride is available in capsule form, tablet form, syrup form, injectable form
(through a muscle or vein), cream form, gel form, stick form, spray form, and in an elixir (a clear, sweet,
part-alcoholic liquid that is taken by mouth) form. It should be taken with milk or a meal to reduce stress on
the digestive system. It is OK to remove the contents from the capsule and take it with water or food.
The skin should be cleaned before applying this medication on the skin in cream form or any other form
that is rubbed on the skin. Do not apply this medication to exposed or blistered skin. If irritation occurs
after using this drug, you should stop using it and contact your doctor.
WHAT ARE SIDE EFFECTS OF DIPHENHYDRAMINE HYDROCHLORIDE?
Common side effects of diphenhydramine hydrochloride are sleepiness, dry mouth, nausea, thickening of
mucus, and anorexia (serious loss in body weight due to refusal to eat). Less common side effects are as
follows: skin rash, rapid heartbeat, hypersensitivity reactions (such as to the light and sun), blurry vision,
ringing in the ears, dizziness, headache, low blood pressure, diarrhea, difficult urination, painful urination,
constipation, and confusion. There are no known special problems associated with long-term use of this
DOES DIPHENHYDRAMINE HYDROCHLORIDE CAUSE BIRTH DEFECTS?
There are no known significant increases in birth defects associated with diphenhydramine hydrochloride
in humans. However, the safety of this drug with pregnant women has not yet been determined. Animal
studies have not found that birth defects are associated with this drug.
WHAT CAN I DO TO AVOID OR DECREASE DRY MOUTH THAT CAN OCCUR BY TAKING THIS
To avoid dry mouth as a result of using diphenhydramine hydrochloride, it is recommended to take
frequent sips of water or to use a sugarless gum and candy. Keeping your mouth clean by brushing your
teeth regularly also helps. If dry mouth continues for more than 2 weeks, you should contact your doctor
WHO SHOULD NOT TAKE DIPHENHYDRAMINE HYDROCHLORIDE?
People with the following conditions should not take diphenhydramine hydrochloride: suddenly occurring
attacks of asthma (difficulty breathing due to narrowing of the airway passage) and hypersensitivity to this
drug. Moms who are secreting (releasing) breast milk should not take diphenhydramine hydrochloride
because it passes into the breast milk. Children under age two should avoid this drug. People who cannot
tolerate alcohol should also avoid this drug if it is taken in a form that includes alcohol, such as a syrup.
WHO SHOULD BE ESPECIALLY CAREFUL WHEN USING DIPHENHYDRAMINE HYDROCHLORIDE?
People who are elderly (over age 60) should be careful when using diphenhydramine hydrochloride
because they are more likely to suffer side effects. It is recommended by many doctors that elderly
patients take lower doses of this drug. Since the safety of diphenhydramine hydrochloride is not
established during pregnancy, pregnant women should also be cautious before taking this medication.
People with the following medical conditions should also be careful when using diphenhydramine
hydrochloride: severe breathing problems, severe liver disease, seizures (involuntary muscle movements
due to overexcitement of nerve cells in the brain), or an enlarged prostate. The prostate is a gland near
the bladder that produces a reproductive fluid.
People with narrow-angle glaucoma should also be careful when using diphenhydramine hydrochloride.
Narrow-angle glaucoma is a sudden, painful condition in the eye as well as blurry vision caused by
increased pressure that is due to a blockage of a watery fluid known as aqueous humor. You should
contact your doctor for advice if you have any of the previously mentioned conditions.
WHAT PRECAUTIONS SHOULD BE TAKEN WITH DIPHENHYDRAMINE HYDROCHLORIDE?
Individuals taking diphenhydramine hydrochloride should avoid direct exposure to the sun and use
sunscreen, since the body can become oversensitive to the effects of this drug when they are exposed to
the sun. Alcohol and other substances that decrease the activity of the brain and spinal cord should also
be avoided, since taking either of them with diphenhydramine hydrochloride can lead to negative
Driving, hazardous work, and other activities requiring alertness should be avoided when taking
diphenhydramine hydrochloride, until you can assess how this drug affects you. Piloting an aircraft is not
allowed when taking this drug.
HOW LONG DOES IT TAKE FOR DIPHENHYDRAMINE HYDROCHLORIDE TO WORK?
When taken by mouth, diphenhydramine hydrochloride works within 15 to 60 minutes. When injected
through a muscle, it takes 20 to 30 minutes to work. When injected through a vein, it works rapidly.
HOW LONG DO THE EFFECTS OF DIPHENHYDRAMINE HYDROCHLORIDE LAST?
The effects of diphenhydramine hydrochloride work for approximately 4 to 8 hours, regardless of the form
it is taken in.
WHEN SHOULD I STOP TAKING DIPHENHYDRAMINE HYDROCHLORIDE?
You should stop taking diphenhydramine hydrochloride if it is not effective after 5 days. You should also
call your doctor at this point if the drug is not working.
HOW IS DIPHENHYDRAMINE HYDROCHLORIDE ABSORBED BY THE BODY?
Diphenhydramine hydrochloride is absorbed well by the body if one takes it by mouth or if it is injected
through a muscle. However, it may not be absorbed well if taken as a cream or as another form that is
rubbed on the skin.
Diphenhydramine hydrochloride is distributed widely throughout the body. It enters into the breast milk and
crosses the placenta (an organ in a female that nourishes a baby during pregnancy). 95% of this drug is
metabolized (chemically processed) by the liver.
DOES DIPHENHYDRAMINE HYDROCHLORIDE INTERACT WITH OTHER DRUGS OR FOODS?
Yes. This is why you should contact your doctor to see what you should do if you are taking other
antihistamines, anticholinergics (drugs that reduce uncontrollable muscle movements by competing with
the chemical messenger, acetylcholine), or central nervous system depressants (drugs that decrease the
activity of the brain and/or spine). Using diphenhydramine hydrochloride with these drugs will further slow
down certain bodily functions.
Diphenhydramine hydrochloride also interacts with disopyramide and quinidine(drugs used to control
abnormal heart beat) as well as antidepressants known as tricyclics and MAO inhibitors. The interaction
between diphenhydramine hydrochloride and these drugs makes side effects such as dry mouth and blurry
Diphenhydramine hydrochloride can lead to excessive sleepiness when taken in combination with the
following: 5-HTP (a chemical supplement believed to improve mood, sleep, pain, and decrease appetite),
GABA (a chemical messenger in the body that sends messages telling it to slow down), kava (an herb
believed to have calming effects), melatonin (a natural chemical in the body thought to promote sleep),
melissa (leaves and flowers of a plant that is thought to have calming effects on the body), and valerian
(an herb thought to help people sleep). Diphenhydramine hydrochloride is not known to interact with any
WHAT IS THE USUAL DOSE FOR DIPHENHYDRAMINE HYDROCHLORIDE?
The dose of diphenhydramine hydrochloride that should be taken varies according to the reason for why
this medication is being taken, the form in which the medication is taken, the age of the person, and the
weight of the person. Following are the doses for diphenhydramine hydrochloride, according to these
HAY FEVER SYMPTOMS (capsules, tablets, elixir, syrup):
Teenagers and adults: 25 to 50 milligrams (mg) very 4 to 6 hours.
Children weighing more than 20.02 pounds: 12.5 to 25 mg every 4 to 6 hours. The total dose per day
should not be more than 300 mg a day.
Children weighing less than 20.02 pounds: 6.25 to 12.5 mg every 4 to 6 hours.
HAY FEVER SYMPTOMS (injection):
Adults: 10 to 50 mg through a vein or muscle, 2-3 times a day. A single dose may be as much as 100
mg, but the total dose per day should not be more than 400 mg.
Children: 1.25 mg per 2.2 pounds (one kilogram) of body weight into a muscle four times a day. The
total dose per day should not be more than 300 mg.
HAY FEVER SYMPTOMS (cream, gel, or stick):
Adults and children 12 years or older: Apply cream, gel, or stick that says "2%," three to four times a
Children ages 6-12 years or older: Apply cream, gel, or stick that says "1%," three to four times a day.
COUGH (liquid form):
Adults and teenagers: 25 mg, every 4 to 6 hours, as needed. The total dose should not be more than
150 mg a day.
Children ages 2 to 6: 6.25 mg (half a teaspoon) every 4 to 6 hours. The total dose should not be more
than 25 mg a day.
Children ages 6 to 12: 12.5 mg (1 teaspoon) to 25 mg (2 teaspoons) every 4 to 6 hours. The total dose
should not be more than 75 mg a day.
NAUSEA, VOMITTING, AND DIZZINESS (capsules, tablets, elixir, syrup):
Adults: 25 to 50 mg every 4 to 6 hours.
Children: 1 to 1.5 mg per 2.2 pounds every 4 to 6 hours.
NAUSEA, VOMITTING, AND DIZZINESS (injection):
Adults: 10 mg through a vein or muscle. This may be increased to 25 to 50 mg every 2 to 3 hours.
Children: 1 to 1.5 mg per 2.2 pounds every 6 hours.
When using diphenhydramine hydrochloride to prevent motion sickness, it should be taken 30 minutes
before traveling and 1 to 2 hours before being exposed to anything that would lead to motion sickness,
such as sitting on a boat before traveling on it.
PARKINSON'S DISEASE (capsules, tablets, elixir, syrup):
Adults: 25 mg, 3 times a day. The doctor may increase the dose slowly over time, but the total dose
should not be more than 400 mg a day.
Children: 1.25 mg per 2.2 lbs into a muscle, four times a day. The total dose should not be more than
300 mg a day.
SLEEPING AND/OR RELAXATION DIFFICULTIES (capsules, tablets, elixir, syrup):
Adults: 50 mg, 20 to 30 minutes before going to bed.
For people who have occasional sleeping difficulties, this medication may be effective when taken only
as needed (for example, only taking it on the night one is having difficulty sleeping). For people with
more serious sleeping problems, this medication may need to be taken on a more regular basis. Such
individuals should consult with their doctor to determine the length of time needed to take this
medication or for a possible change to another sleep medication.
WHAT IF I MISS A DOSE?
If you miss a dose of diphenhydramine hydrochloride, you should check with your doctor. Doctors
generally recommend that you take it again as soon as you can. However, if this time is near your next
scheduled dose, doctors generally recommend skipping the dose that was missed and not doubling the
WHAT ARE SYMPTOMS OF AN OVERDOSE OF DIPHENHYDRAMINE HYDROCHLORIDE AND WHAT
SHOULD I DO?
Symptoms of an overdose of diphenhydramine hydrochloride include: being very sleepy, wide pupils (the
black circle in the eyeball) that do not decrease in size in response to light, confusion, difficulty breathing,
being excited easily, poor coordination, weak pulse, passing out, and seizures (involuntary muscle
movements due to overexcitement of nerve cells in the brain). When an overdose occurs, the Emergency
Medical Service (EMS) or the nearest poison control center should be called immediately. If in doubt of
where to call, dial 911.
DOES DIPHENHYDRAMINE HYDROCHLORIDE INTERFERE WITH ANY LABARATORY TESTS?
Yes. If you are going to have your skin tested for an allergic reaction, then diphenhydramine hydrochloride
can interfere with such a test. If this is the case, this medication should be stopped four days before
taking such a skin test.
WHERE SHOULD DIPHENHYDRAMINE HYDROCHLORIDE BE STORED?
Diphenhydramine hydrochloride should be stored in a dry place and should be kept away from heat and
direct light. Liquid forms should not be frozen.
WHAT ELSE IS DIPHENHYDRAMINE HYDROCHLORIDE KNOWN AS?
Diphenhydramine hydrochloride has been trademarked (given brand names) by several companies. These
names are as follows: Allerdryl, AllerMax, Aller-med, Banophen, Beldin, Beldin Cough, Belix, Bena-D,
Bena-D 50, Benadryl, Benadryl Itch Relief Children's, Benadryl Complete Allergy, Benadryl Dye-Free
Allergy Medication, Benadryl Itch Stopping Gel Children's Formula, Benadryl Itch Stopping Gel Maximum
Strength, Benahist, Ben-Allergin, Ben-Allergin 50, Benaphen, Benoject, Benylin Cough, Bydramine Cough,
Compoz, Diahist, Dihydrex, Diphen-Cough, Diphenacen-10, Diphenacen, Diphenadryl, Diphenhist,
Dormarex 2, Dormin, Fenylhist, Fynex, Genahist, Gen-D-Phen, Hydramine, Hydramyn, Hydril, Hyrexin,
Hyrexin-50, Insomnal, Maximum Strength Benadryl Itch Relief, Miles Nervine, Nauzene Maximum Strength,
Nervine Nighttime Sleep-Aid, Nidryl, Noradyl, Nordryl, Nordryl Cough, Nytol, Nytol Extra Strength, Nytol
Maximum Strength, Nyto with DPH, Phendry, PMS-Diphenhydramine, Siladril, Silphen, Sleep-Eze D, Sleep-
Eze D Extra Strength, Sleep-Eze 3, Sleepwell 2-nite, Sominex, Sominex Formula 2, Tusstat, Twilite, Uni-
Bent Cough, Unisom SleepGels Maximum Strength, Valdrene, and Wehdryl.
Diphenhydramine hydrochloride can be purchased in your local drug store under one of the previously
mentioned trademarked names. By law, the brand name versions of a generic drug all need to have the
same ingredients as the generic version. The only difference between medications with brand names and
those without brand names is the price.
WHY IS IT CALLED DIPHENHYDRAMINE HYDROCHLORIDE?
The chemical name for diphenhydramine hydrochloride is 2-(Diphenylmethoxy)-N,N-dimethylethylamine
hydrochloride. By looking at the letters in purple, you can tell how diphenhydramine hydrochloride got its