- 10 Common Allergy Triggers Slideshow Pictures
- Take the Quiz on Allergies
- Nasal Allergy Relief Products Slideshow
- What is diphenhydramine, and how does it work (mechanism of action)?
- What are the side effects of diphenhydramine?
- What is the dosage for diphenhydramine?
- Which drugs or supplements interact with diphenhydramine?
- Is diphenhydramine safe to take if I'm pregnant or breastfeeding?
- What else should I know about diphenhydramine?
What is diphenhydramine, and how does it work (mechanism of action)?
Diphenhydramine is an antihistamine used for treating allergic reactions. Histamine is released by the body during several types of allergic reactions and--to a lesser extent--during some viral infections, such as the common cold. When histamine binds to receptors on cells, it stimulates changes within the cells that lead to the release of chemicals that cause sneezing, itching, and increased mucus production. Antihistamines compete with histamine for cell receptors and bind to the receptors without stimulating the cells. In addition, they prevent histamine from binding and stimulating the cells. Diphenhydramine also blocks the action of acetylcholine (anticholinergic effect) and is used as a sedative because it causes drowsiness. The FDA originally approved diphenhydramine in 1946.
Benadryl, Sominex, Unisom, Nytol, and several others
No. Yes (Injection)
What are the side effects of diphenhydramine?
Diphenhydramine commonly can cause:
- disturbed coordination,
- drying and thickening of oral and other respiratory secretions, and
- urinary retention.
Diphenhydramine also may cause
- low blood pressure,
- palpitations (abnormal heartbeats),
- increased heart rate,
- blurred vision,
- double vision,
- painful urination or difficulty urinating,
- loss of appetite,
- erectile dysfunction, and
Diphenhydramine should be used with caution (if at all) in persons with narrow-angle glaucoma, prostatic hypertrophy (enlarged prostate gland), hyperthyroidism, cardiovascular disease, high blood pressure (hypertension), and asthma.
What is the dosage for diphenhydramine?
Diphenhydramine doses vary depending on formulation, and has its maximal effect about one hour after it is taken.
- When used to treat insomnia, it is prescribed at bedtime. Indivduals over the age of 60 years are especially sensitive to the sedating and anticholinergic effects of diphenhydramine, and the dose should be reduced.
- A common regimen for treating adult allergic reaction is 25-50 mg every 4-6 hours not to exceed 300 mg daily.
- Insomnia is treated with 50 mg taken 30 minutes before bedtime.
Which drugs or supplements interact with diphenhydramine?
Diphenhydramine adds to (exaggerates) the sedating effects of alcohol and other drugs than can cause sedation such as the benzodiazepine class of anti-anxiety (for example, diazepam [Valium], lorazepam [Ativan], clonazepam [Klonopin], alprazolam [Xanax]), the narcotic class of pain medications and its derivatives (for example, oxycodone and acetaminophen [Percocet], and hydrocodone and acetaminophen [Vicodin], guaifenesin with hydromorphone [Dilaudid], codeine, propoxyphene [Darvon]), the tricyclic class of antidepressants (for example, amitriptyline [Elavil, Endep], imipramine [Tofranil], desipramine [Norpramin]), and certain antihypertensive medications (for example, clonidine [Catapres], propranolol [Inderal]). Diphenhydramine also can intensify the drying effects of other medications with anticholinergic properties (for example, dicyclomine [Bentyl] and bethanechol [Urecholine], probanthine).
Is diphenhydramine safe to take if I'm pregnant or breastfeeding?
Diphenhydramine has not been adequately evaluated in pregnant women. It should be used only if the benefit outweighs the potential but unknown risks.
NURSING MOTHERS: Diphenhydramine is secreted in breast milk. Because of the risk of stimulation and seizures in infants, especially newborns and premature infants, antihistamines should not be used by nursing mothers.
What else should I know about diphenhydramine?
What preparations of diphenhydramine are available?
- Capsules: 25 and 50 mg. Tablets: 12.5, 25 and 50 mg.
- Tablet (Chewable or dispersible)): 12.5 mg.
- Strips: 12.5 and 25 mg.
- Elixir, oral solution, liquid: 12.5 mg per teaspoon (5 mL).
- Strip: 25 mg. Injection: 50 mg per ml.
How should I keep diphenhydramine stored?
Diphenhydramine should be stored at room temperature, 15 C to 30 C (59 F to 86 F), and the injection should be protected from freezing and light.
Latest Allergies News
Daily Health News
Multimedia: Slideshows, Images & Quizzes
Allergies Quiz: Symptoms & Home Remedies
What are the causes of allergies? This online quiz challenges your knowledge of common food and household allergens,...
Atopic Eczema (Atopic Dermatitis) Quiz: Test Your Skin Disorders IQ
Does dry, itchy, flaky, scaly, red, inflamed skin sound familiar to you? Take the Atopic Eczema (Atopic Dermatitis) Quiz to learn...
Chickenpox Quiz: Test Your Medical IQ
How is chickenpox related to shingles? Take the Chickenpox Quiz to assess your IQ of this itchy, blistering childhood skin...
Bed Bugs Quiz: How to Get Rid of Bed Bugs
That unexplained itching could be caused by bedbugs. Take the Bedbugs Quiz to learn the causes and symptoms of a bedbug...
Sleep Quiz: Sleep Hygiene & Sleep Facts
Take our Sleeping Quiz to learn which sleep disorders, causes, and symptoms rule the night. Trouble falling or staying asleep?...
Picture of Fixed Drug Eruption
A large red-violet plaque on the arm of a child. See a picture of Fixed Drug Eruption and learn more about the health topic.
Picture of Urticaria
This is a close-up view of wheals with white-to-light-pink color centrally and peripheral erythema. See a picture of Urticaria...
What Is Scabies? Rash, Treatment, Symptoms, Pictures
Get the facts on scabies (itch mite) causes, signs and symptoms. Learn what scabies looks like and how to treat it through these...
Related Disease Conditions
Insect Sting Allergies
The majority of stinging insects in the United States are from bees, yellow jackets, hornets, wasps, and fire ants. Severity of reactions to stings varies greatly. Avoidance and prompt treatment are essential. In selected cases, allergy injection therapy is highly effective.
Allergy Treatment Begins At Home
Avoiding allergy triggers at home is one of the best ways to prevent allergy symptoms. Controlling temperature, humidity, and ventilation are a few ways to allergy-proof the home. Cleaning, vacuuming, and using HEPA air filters also helps control allergies.
Canker sores are a common complaint, and are small ulcers on the inside of the mouth. Canker sores aren't contagious (as opposed to cold sores), and typically last for 10-14 days usually healing without scarring. A variety of things cause canker sores, for example, medications (aspirin, beta-blockers, NSAIDs, high blood pressure medication, and antibiotics); injury to the mouth from dental work, braces, or sports accidents; acidic foods; allergies; and diseases or conditions like celiac disease, Crohn's disease, and lupus. Canker sores can be cure with home remedies, and prescription and OTC topical and oral medication.
19 Tips on How to Stop a Cough
Coughing is a reflex that helps a person clear their airways of irritants. There are many causes of an excessive or severe cough including irritants like cigarette and secondhand smoke, pollution, air fresheners, medications like beta blockers and ACE inhibitors, the common cold, GERD, lung cancer, and heart disease. Natural and home remedies to help cure and soothe a cough include stay hydrated, gargle saltwater, use cough drops or lozenges, use herbs and supplements like ginger, mint, licorice, and slippery elm, and don't smoke. Over-the-counter products (OTC)to cure and soothe a cough include cough suppressants and expectorants, and anti-reflux drugs. Prescription drugs that help cure a cough include narcotic medications, antibiotics, inhaled steroids, and anti-reflux drugs like proton pump inhibitors or PPIs, for example, omeprazole (Prilosec), rabeprazole (Aciphex), and pantoprazole (Protonix).
Flea Bites (In Humans)
Flea bites are caused by the parasitic insect, the flea. The most common species of flea in the US is the cat flea, Ctenocephalides felis. Signs and symptoms of flea bites in humans include itching, hives, a rash with bumps, red spots with a "halo," and swelling around the bite. Treatment for flea bites includes over-the-counter medicine and natural and home remedies to relieve and soothe itching and inflammation. The redness of a flea bite can last from a few hours to a several days.
Inner Ear Infection (Symptoms, Signs, Treatments, Home Remedies)
An inner ear infection or otitis interna is caused by viruses or bacteria and can occur in both adults and children. An inner ear infection can cause symptoms and signs, for example, a severe ear, dizziness, vertigo, nausea and vomiting, and vertigo. An inner ear infection also may cause inflammation of the inner ear or labyrinthitis. Inner ear infections are not contagious; however, the bacteria and viruses that cause the infection can be transmitted to other people. Good hygiene practices will help decrease the chances of the infection spreading to others. Inner ear infection symptoms and signs like ear pain and nausea may be relieved with home remedies or over the counter (OTC) medication. Some inner ear infections will need to be treated and cured with antibiotics or prescription pain or antinausea medication.
Chronic Rhinitis and Post-Nasal Drip
Chronic rhinitis and post-nasal drip symptoms include an itchy, runny nose, sneezing, itchy ears, eyes, and throat. Seasonal allergic rhinitis (also called hay fever) usually is caused by pollen in the air. Perennial allergic rhinitis is a type of chronic rhinitis and is a year-round problem, often caused by indoor allergens, such as dust, animal dander, and pollens that may exist at the time. Treatment of chronic rhinitis and post nasal drip are dependent upon the type of rhinitis condition.
Hives (Urticaria & Angioedema)
Hives, also called urticaria, is a raised, itchy area of skin that is usually a sign of an allergic reaction. The allergy may be to food or medications, but usually the cause of the allergy (the allergen) is unknown.
Itch (Itching or Pruritus)
Itching can be a common problem. Itches can be localized or generalized. There are many causes of itching to include: infection (jock itch, vaginal itch), disease (hyperthyroidism, liver or kidney), reactions to drugs, and skin infestations (pubic or body lice). Treatment for itching varies depending on the cause of the itch.
Shingles, or herpes zoster, is a painful rash caused by the varicella zoster virus. Other shingles symptoms include headache, fever, nausea, and body aches. Treatment focuses on pain management and shortening the duration of the illness with antiviral medications.
Ticks are known transmitters of disease to humans and animals. Tick-borne diseases include Lyme disease, Rocky Mountain spotted fever, Q fever, tularemia, babesiosis, and Southern tick-associated rash illness. Infected ticks spread disease once they've bitten a host, allowing the pathogens in their saliva and mouth get into the host's skin and blood. Tick bites are typically painless, but the site of the bite may later itch, burn, turn red, and feel painful. Individuals allergic to tick bites may develop a rash, swelling, shortness of breath, numbness, or paralysis. Tick bite treatment involves cleaning and applying antibiotic cream.
Poison ivy, oak, and sumac contain a substance called urushiol, which causes a rash on people who come in contact with them. Symptoms and signs include a red, swollen, itchy, blistering, bumpy rash. Treatment involves rinsing the exposed area with water, taking antihistamines and over-the-counter pain medications, using topical treatments such as calamine lotion, and applying cool compresses.
Vaginal Pain (Vulvodynia)
Vulvodynia or vaginal pain, genital pain is a condition in which women have chronic vulvar pain with no known cause. There are two types of vulvodynia, generalized vulvodynia and vulvar vestibulitis. Researchers are trying to find the causes of vulvodynia, for example, nerve irritation, genetic factors, hypersensitivity to yeast infections, muscle spasms, and hormonal changes.The most common symptoms of vaginal pain (vulvodynia) is burning, rawness, itching, stinging, aching, soreness, and throbbing. There are a variety of treatments that can ease the symptoms of vulvodynia (vaginal pain).
Eustachian Tube Dysfunction
The Eustachian tube is a membrane lined tube that connects the middle ear space to the back of the nose. Symptoms of Eustachian tube dysfunction or blockage include popping and/or clicking in the ear, and ear fullness and/or pain. Causes of Eustachian tube dysfunction or blockage include allergies, sinus infections, ear infections, and the common cold. Treatment includes home remedies to relieve pain and several maneuvers (swallowing, chewing gum, yawning etc.), which can be done to improve Eustachian tube function. In severe cases surgery may be necessary.
An allergy refers to a misguided reaction by our immune system in response to bodily contact with certain foreign substances. When these allergens come in contact with the body, it causes the immune system to develop an allergic reaction in people who are allergic to it. It is estimated that 50 million North Americans are affected by allergic conditions. The parts of the body that are prone to react to allergies include the eyes, nose, lungs, skin, and stomach. Common allergic disorders include hay fever, asthma, allergic eyes, allergic eczema, hives, and allergic shock.
Pityriasis rosea is a rash that begins with a large pink patch with well-defined scaly borders on the back, chest, or neck. In one to two weeks, the person will develop many smaller pink patches on his or her trunk, arms, and legs. Symptoms include mild itching and possible sore throat, fatigue, nausea, aching, and decreased appetite. Pityriasis rosea typically resolves on its own and symptoms and signs may be treated with topical steroid creams and oral antihistamines.
Inner Ear Infection (Labyrinthitis)
Labyrinthitis is inflammation of the labyrinth (the part of the ear responsible for balance and hearing). Doctors do not know the exact cause of labyrinthitis; however, they often are associated viral infections of the inner ear. Symptoms of labyrinthitis are ear pain or earache, ear discharge, problems with balance and walking, ringing in the ears, dizziness, nausea, vomiting, and vertigo. Viral infections associated with labyrinthitis are contagious. Home remedies may help labyrinthitis symptoms and signs. Over-the-counter (OTC) and prescription medication may treat inner ear infections, labyrinthitis symptoms like vertigo and nausea, and help ear pain.
Urinary retention (inability to urinate) may be caused by nerve disease, spinal cord injury, prostate enlargement, infection, surgery, medication, bladder stone, constipation, cystocele, rectocele, or urethral stricture. Symptoms include discomfort and pain. Treatment depends upon the cause of urinary retention.
Medical shock is a life-threatening medical condition. There are several types of medical shock, including: septic shock, anaphylactic shock, cardiogenic shock, hypovolemic shock, and neurogenic shock. Causes of shock include: heart attack, heart failure, heavy bleeding (internal and external), infection, anaphylaxis, spinal cord injury, severe burns, chronic vomiting or diarrhea. Low blood pressure is the key sign of sock. Treatment is dependant upon the type of shock.
Eczema refers to skin inflammation. There are many different types of eczema that produce symptoms and signs that range from oozing blisters to crusty plaques of skin. Treatment varies depending upon the type of eczema the person has.
Scabies are itch mites that burrow under the skin and produce intense itching that's usually worse at night. Symptoms of scabies are small bumps and blisters on the wrists, knees, between the fingers, on the back of the elbows, in the groin and on the buttocks. Treatment involves applying a mite-killing cream, antihistamines for itch relief, washing bedclothes and linens.
Parkinson's disease is a slowly progressive neurological disease characterized by a fixed inexpressive face, a tremor at rest, slowing of voluntary movements, a gait with short accelerating steps, peculiar posture and muscle weakness, caused by degeneration of an area of the brain called the basal ganglia, and by low production of the neurotransmitter dopamine. Most patients are over 50, but at least 10 percent are under 40.
Chickenpox (chicken pox) is a contagious childhood disease caused by the varicella-zoster virus. Symptoms have an incubation period of 14 to 16 days and include a couple days of mild fever, weakness, and red, raised rash that progresses to blisters that eventually burst and crust over. Complications include bacterial infection of the open sores, scarring, encephalitis, nerve palsies, and Reye's syndrome.
Coxsackieviruses may be divided into two groups. Type A causes hand, foot, and mouth disease and conjunctivitis, while type B causes pleurodynia. Both types sometimes cause meningitis, myocarditis, and pericarditis. There is no specific treatment for this disease.
About 1% to 2% of people in the U.S. have a peanut allergy. Symptoms and signs of a peanut allergy include rash, hives, redness, and itching. Severe reactions may cause difficulty breathing, nausea, decreased blood pressure, lightheadedness, and behavioral changes. People with a peanut allergy should carry an epinephrine auto-injector with them at all times.
Shingles and Pregnancy
Becoming infected with chickenpox during pregnancy could cause birth defects in your unborn child. Likewise, shingles could also cause problems for your unborn child. If you are pregnant and haven't had chickenpox, avoid exposure to infected people. Zostavax, the shingles vaccine, can reduce the incidence of shingles by half. Women should wait at least three months after receiving the vaccine before trying to get pregnant.
Sleep Disorders (How to Get a Good Night's Sleep)
A number of vital tasks carried out during sleep help maintain good health and enable people to function at their best. Sleep needs vary from individual to individual and change throughout your life. The National Institutes of Health recommend about 7-9 hours of sleep each night for older, school-aged children, teens, and most average adults; 10-12 for preschool-aged children; and 16-18 hours for newborns. There are two stages of sleep; 1) REM sleep (rapid-eye movement), and 2) NREM sleep (non-rapid-eye movement). The side effects of lack of sleep or insomnia include: Irritability Tiredness Feeling sleepy during the day Concentration or memory problems Lack of sleep and insomnia can be caused by medical conditions or diseases, medications, stress, or pain. The treatment for lack of sleep and insomnia depends upon the cause.
Hay Fever (Allergic Rhinitis)
Hay fever (allergic rhinitis) is an irritation of the nose caused by pollen and is associated with the following allergic symptoms: nasal congestion, runny nose, sneezing, eye and nose itching, and tearing eyes. Avoidance of known allergens is the recommended treatment, but if this is not possible, antihistamines, decongestants, and nasal sprays may help alleviate symptoms.
Insomnia (Symptoms, Causes, Remedies, and Cures)
Insomnia is the perception or complaint of inadequate or poor-quality sleep because of difficulty falling asleep; waking up frequently during the night with difficulty returning to sleep; waking up too early in the morning; or unrefreshing sleep. Secondary insomnia is the most common type of insomnia. Treatment for insomnia include lifestyle changes, cognitive behavioral therapy, and medication.
Are Hives (Urticaria) Contagious?
Hives are not contagious are triggered by an allergic response to a substance. Symptoms and signs of hives include a raised, itchy red rash on the skin. An individual should seek medical care for hives if he or she develops dysphagia, wheezing, shortness of breath, or throat tightening.
Ciguatera poisoning is a type of food poisoning caused by the ciguatera toxin found in a variety of large reef fish found between the Tropic of Cancer and the Tropic of Capricorn. Symptoms of ciguatera poisoning include diarrhea, nausea, vomiting, abdominal pain, dizziness, vertigo, numbness, tingling, and muscle pain. Ciguatera poisoning requires medical treatment.
Zika Virus (Zika Fever)
The Zika virus is transmitted by the bite of an infected Aedes mosquito. Symptoms and signs of a Zika virus infection include conjunctivitis, headache, joint pain, fever, rash, and muscle aches. Treatment for Zika virus infections aims to alleviate symptoms.
Teen Drug Abuse
Drugs commonly abused by teens include tobacco products, marijuana, cold medications, inhalants, depressants, stimulants, narcotics, hallucinogens, PCP, ketamine, Ecstasy, and anabolic steroids. Some of the symptoms and warning signs of teen drug abuse include reddened whites of eyes, paranoia, sleepiness, excessive happiness, seizures, memory loss, increased appetite, discolored fingertips, lips or teeth, and irritability. Treatment of drug addiction may involve a combination of medication, individual, and familial interventions.
Insomnia Treatment (Sleep Aids and Stimulants)
Insomnia is difficulty in falling or staying asleep, the absence of restful sleep, or poor quality of sleep. Insomnia is a symptom and not a disease. The most common causes of insomnia are medications, psychological conditions, environmental changes and stressful events. Treatments may include non-drug treatments, over-the-counter medicines, and/or prescription medications.
Treatment & Diagnosis
- Inner Ear Infection (Otitis Interna)
- Bug Bites and Stings
- Poison Ivy, Oak, and Sumac
- Doctor: Checklist to Take To Your Doctor's Appointment
- Red Spots on the Skin
- Bee and Wasp Sting
- Motion Sickness
- Runny Nose
- Swollen Tongue
- Nasal Congestion
- Swollen Lip
- Postnasal Drip
- Bed Bugs FAQs
- Allergies FAQs
- Sleep FAQs
- Chickenpox FAQs
- Eczema FAQs
- How To Reduce Your Medication Costs
- Pharmacy Visit, How To Get The Most Out of Your Visit
- Indications for Drugs: Approved vs. Non-approved
- Drugs: Buying Prescription Drugs Online Safely
- Drugs: The Most Common Medication Errors
- Travel Medicine Kit
- Medication Disposal
- Dangers of Mixing Medications
- OTC Cold and Cough Medications
- Bug Bite Treatment
- Generic Drugs, Are They as Good as Brand-Names?
Medications & Supplements
- chlordiazepoxide hydrochloride and clidinium bromide (Librax)
- chlorpheniramine, pseudoephedrine
- hydroxyzine (Vistaril)
- Antihistamines (Oral)
- Anticholinergic and Antispasmodic Drugs
- Drugs: Questions to Ask Your Doctor or Pharmacist about Your Drugs
- Hypnotics (for Sleep)
- Nasal Allergy Medications
- Drug Interactions
Prevention & Wellness
- Are Too Many Kids Prescribed Antihistamines?
- Widely Prescribed Class of Meds Might Raise Dementia Risk
- Many Misuse OTC Sleep Aids: Survey
- Common Meds and Dementia: How Strong Is the Link?
- Fridge-Sized Machine Makes Prescription Drugs 'On Demand'
- Kids' ER Visits for Medicine Overdoses Dropping: Report
- Are We Taking Some Medicines for Too Long?
- Health Tip: Dealing With a Bee Sting
- Certain Allergy, Depression Meds Tied to Higher Odds for Dementia
- Anxiety Medications May Be Tied to Alzheimer's Risk
- Sizing Up Your Options for Hay Fever Relief
- Antihistamines Adding to Drug Pollution in Streams
- Health Tip: Using an Antihistamine
- Sleepwalking May Be More Common Than You Think
- Sleeping Pills Called 'as Risky as Cigarettes'
- FDA: Don't Swallow Benadryl Gel
- FDA: Manufacturing Problems Led to Tylenol Recall
- Recall of Kids' Tylenol, Motrin, Zyrtec, Benadryl
- Spring Allergy Relief Can Be Hard to Find
Health Solutions From Our Sponsors
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.