Diphenhydramine is a first-generation antihistamine used for symptoms of allergies and colds, such as sneezing, runny nose, or skin rash. It is also used to induce sleep, motion sickness, and some symptoms of Parkinson's disease. It should be used with caution since it causes dizziness and drowsiness.

Diphenhydramine brand names

Diphenhydramine is available under the brand names Benadryl, Benadryl Allergy, Genahist, Sominex, Banophen, ZzzQuil, Diphenhist, Restamin, Complete Allergy Medicine, Resmin, Ziradryl, Quiet World, Prodryl, Allermax, Diphen, Children’s Allergy, and others.

What is diphenhydramine prescribed for?

Diphenhydramine is used to treat the symptoms of colds and allergies, such as sneezing, runny nose, watery red, itchy or irritated eyes, hives, rashes, and other signs of hay fever, including urticaria and pruritis. It is also used to relieve coughs caused by allergies or airway irritation, resulting in wheezing.

This medicine is also used to treat and prevent motion sickness. It is also used to treat those adults with difficulty falling asleep or staying asleep.

Diphenhydramine relieves the symptoms of involuntary movements (also called extrapyramidal reactions) in people with early-stage Parkinson’s disease who experience a lack of muscle control and balance as a side effect of their medications.[1] It is also used in the elderly with Parkinson’s disease who do not tolerate other drugs and in mild cases in younger age groups.

How does diphenhydramine work?

Diphenhydramine is an antihistamine, meaning that it blocks the action of histamine in the body. Histamine is part of the defense system of our bodies. It is a chemical released by the body in response to what it perceives as a foreign substance (allergen) in the body (e.g., pollen, dust). These chemical signal responses can occur in the lungs, skin, nose, mouth, gut, and blood.[2]

How is diphenhydramine usually taken?

The dose of diphenhydramine that needs to be taken depends on the symptom/s it is treating. Different brand names will contain diphenhydramine as hydrochloride or citrate, influencing the dose needed. Never take more or less than prescribed without medical advice.

The following doses comprise of oral formulations, i.e., tablets or syrups. Diphenhydramine is sometimes also administered as an intravenous (IV) formulation by a healthcare professional, usually in a hospital setting.[3]

Extrapyramidal reactions

Adults:

Diphenhydramine Hydrochloride 25mg to 50mg tablet taken every six to eight hours

Insomnia

Adults:

Diphenhydramine Hydrochloride 50mg once a day, half an hour before bedtime.

Children:

Only given over 12 years of age.

Diphenhydramine Hydrochloride 50mg once a day, half an hour before bedtime.

Motion Sickness

Adults:

Diphenhydramine Hydrochloride 25mg to 50mg orally, the first dose taken half an hour before travel and repeated before meals between six to eight hours later, including at bedtime, for the entire journey duration. Caution should be exercised as the medication may cause drowsiness.

Children:

From one month up:

Oral: 12.5 to 25 mg orally every six to eight hours daily, with the first dose given half an hour before travel time.

Some doctors prefer to prescribe this medication by weight-based dosing of 5 mg/kg orally daily. The maximum dose is 300 mg/day.

Diphenhydramine Hydrochloride:

2 to 6 years: 6.25 mg orally every 4 to 6 hours, with the first dose given half an hour before travel time, with a maximum amount of 37.5 mg/day.

6 to 12 years: 12.5 mg to 25 mg orally every 4 to 6 hours, with the first dose given half an hour before travel time and a maximum amount of 150 mg/day.

12 years and older: 25 mg to 50 mg orally every 4 to 6 hours, the first dose given half an hour before travel time, and a maximum dose of 300 mg/day.

Allergic Rhinitis/Hay Fever

Adults:

Diphenhydramine Hydrochloride 25 to 50mg orally every four to six hours when needed. The maximum dose is 300mg/day.

Children:

From one month up:

Oral: 12.5 to 25 mg orally every six to eight hours daily.

Some doctors prefer to prescribe this medication by weight-based dosing of 5 mg/kg orally daily. The maximum dose is 300 mg/day.

Diphenhydramine Hydrochloride:

2 to 6 years: 6.25 mg orally every 4 to 6 hours as needed, with a maximum dose of 37.5 mg/day.

6 to 12 years: 12.5 to 25 mg orally every 4 to 6 hours as needed, with a maximum dose of 150 mg/day.

12 years and older: 25 to 50 mg orally every 4 to 6 hours as needed, with a maximum dose of 300 mg/day.

Cold Symptoms

Adults:

Diphenhydramine Hydrochloride 25 to 50mg orally every four to six hours when needed. The maximum dose is 300mg/day.

Children:

From one month up:

Oral: 12.5 to 25 mg orally every six to eight hours daily.

Some doctors prefer to prescribe this medication by weight-based dosing of 5 mg/kg orally daily. The maximum dose is 300 mg/day.

Diphenhydramine Hydrochloride:

2 to 6 years: 6.25 mg orally every 4 to 6 hours as needed, with a maximum dose of 37.5 mg/day.

6 to 12 years: 12.5 to 25 mg orally every 4 to 6 hours as needed, with a maximum dose of 150 mg/day.

12 years and older: 25 to 50 mg orally every 4 to 6 hours as needed, with a maximum dose of 300 mg/day.

Pruritis/Itchy Skin

Adults:

Diphenhydramine Hydrochloride 25 to 50mg orally every four to six hours when needed. The maximum dose is 300mg/day.

Children can sometimes get symptoms as a reaction to food:

12.5 mg to 25 mg orally every 4 to 6 hours, or according to weight, with a dose of 5mg/kg per day and a maximum amount of 300 mg/day.

Urticaria/Hives

Adults:

Diphenhydramine Hydrochloride 25 to 50mg orally every four to six hours when needed. The maximum dose is 300mg/day.

Children can sometimes get symptoms as a reaction to food:

12.5 mg to 25 mg orally every 4 to 6 hours, or according to weight, with a dose of 5mg/kg per day and a maximum amount of 300 mg/day.

How long does diphenhydramine stay in your system?

Diphenhydramine stays in the system for about two days. After about 2.4-9.3 hours, half of the dose will be eliminated from the body, and the drug will be completely flushed out within 13.2 to 49 hours. After one or two days, it will no longer be detected in urine; after three to four days, it will not be detected in the blood or saliva. However, the hair follicle may still contain traces of diphenhydramine for ninety days after intake.[4]

Diphenhydramine side effects

Even though diphenhydramine is used to treat allergy symptoms, there may still be an allergic reaction to it. This may show up as difficulty breathing, swelling of the face, throat, lips, and tongue, or hives. If you experience these symptoms and any of the following, you should stop taking the medication and get immediate medical attention:

  • Fast heartbeat or a fluttering feeling in the chest
  • Confusion
  • Feeling faint
  • Tightness in the jaw or neck or uncontrollable movements of the tongue
  • Painful, difficult, decreased or lack of urination

Common side effects of diphenhydramine include:

  • Dry mouth, nose, and throat
  • Constipation
  • Upset stomach
  • Dizziness and drowsiness, including a hangover feeling in the morning after nighttime use
  • Dry eyes or blurred vision
  • Dizziness and lack of coordination[5]

Diphenhydramine precautions

Diphenhydramine should be used with caution in the following conditions:

  • Respiratory depression
  • Liver disease
  • Kidney disease
  • Depression
  • Asthma/Chronic Obstructive Pulmonary Disease (COPD)
  • Cardiovascular problems
  • Glaucoma

Diphenhydramine interactions

Always ask your doctor before taking diphenhydramine with other medications, including over-the-counter medicines, supplements, and vitamins. Alcohol use may increase drowsiness and dizziness with diphenhydramine.

Major drug interactions include[6]:

  • Anticholinergics e.g. clozapine, oxybutynin
  • Sleep medications
  • Cold and flu medications
  • Opioids, e.g. Tramadol
  • Benzodiazepines e.g. alprazolam
  • Certain antidepressants, such as those classified as SSRIs, SNRIs, TCAs, or MAOIs
  • Muscle relaxants

Diphenhydramine storage

This medication should be stored at room temperature in a cool and dry place away from excess heat and moisture. It should be kept in the container it came in. It is essential to keep the medication out of sight and reach of children.

What to do if you overdose on diphenhydramine

Symptoms of a diphenhydramine overdose include anxiety, stomach pain, dry mouth, dilated pupils, blurred vision, dizziness, confusion, and lack of coordination. In severe cases, an overdose can cause seizures, coma, and death.

If you suspect that someone has overdosed on diphenhydramine, it is crucial to seek medical attention immediately. Treatment will typically involve supportive care and may also require using activated charcoal or other medications to reduce the absorption of the drug.[7]

FAQ's

Is diphenhydramine safe during pregnancy?

Since there is no controlled data regarding the use of diphenhydramine during pregnancy, it is best to consult your doctor before use. However, your doctor may suggest an alternative medicine that has been tested and is safer to use at this time.

Is diphenhydramine addictive?

Yes, there is a risk of developing an addiction to diphenhydramine if the medication is abused and not taken as directed by a healthcare professional. When diphenhydramine becomes a means of producing a certain feeling or as a way to escape, this is considered an addiction, even though it is readily available as an over-the-counter medication.

Those with an addiction to diphenhydramine may suffer from increasing adverse effects and worsening insomnia. They may become irritable or depressed, continuing to take the medication even though their allergy or cold symptoms may be long gone.

Abuse and misuse of diphenhydramine can lead to physical and psychological symptoms that affect daily life and work. The patient may suffer from increased anxiety, fast heartbeat, memory loss, and difficulty focusing.[8]

Resources:

  1. Diphenhydramine: MedlinePlus Drug Information. (n.d.). Retrieved October 24, 2022, from https://medlineplus.gov/druginfo/meds/a682539.html
  2. Antihistamines for allergies. (n.d.). https://medlineplus.gov/ency/patientinstructions/000549.htm
  3. Diphenhydramine Dosage Guide + Max Dose, Adjustments. (n.d.). Drugs.Com. Retrieved October 24, 2022, from https://www.drugs.com/dosage/diphenhydramine.html
  4. Benadryl Half-Life: How Long Does it Stay In the System? (n.d.). Addiction Resource. Retrieved October 24, 2022, from https://addictionresource.com/drugs/benadryl/how-long-stays-in-system/
  5. Diphenhydramine Uses, Dosage & Side Effects. (n.d.). Drugs.Com. Retrieved October 24, 2022, from https://www.drugs.com/diphenhydramine.html
  6. Watch Out for These 7 Benadryl Drug Interactions. (n.d.). GoodRx. Retrieved October 24, 2022, from https://www.goodrx.com/diphenhydramine/interactions
  7. Diphenhydramine Overdose: Causes, Signs, And Dangers. (n.d.). Addiction Resource. Retrieved October 21, 2022, from https://addictionresource.com/drugs/benadryl/overdose/
  8. Benadryl Addiction—Is Dyphenhydramine Addictive? (2019, August 19). Addiction Resource. https://www.addictionresource.net/blog/benadryl-addiction/