Definition

Diphenhydramine is a type of medicine called an antihistamine. It is used in some allergy and sleep medicines.

Overdose occurs when someone takes more than the normal or recommended amount of this medicine. This can be by accident or on purpose.

This article is for information only. DO NOT use it to treat or manage an actual overdose. If you or someone you are with has an overdose, call your local emergency number (such as 911), or your local poison control center can be reached directly by calling the national toll-free Poison Help hotline (1-800-222-1222) from anywhere in the United States.

Alternative Names

Benadryl overdose; Sominex overdose; Nytol overdose

Poisonous Ingredient

Diphenhydramine can be harmful in large amounts.

Where Found

Diphenhydramine may be found in many medicines, including those with these brand names:

• Benadryl
• Nytol
• Sominex
• Tylenol PM

Symptoms

Below are symptoms of a diphenhydramine overdose in different parts of the body.

BLADDER AND KIDNEYS

• Inability to urinate

EYES, EARS, NOSE, MOUTH, AND THROAT

• Blurred vision
• Dry mouth
• Enlarged pupils
• Very dry eyes
• Ringing in the ears

HEART AND BLOOD VESSELS

• Low blood pressure
• Rapid heartbeat

NERVOUS SYSTEM

• Agitation
• Confusion
• Seizures
• Delirium
• Depression
• Drowsiness
• Hallucinations (seeing or hearing things that aren't there)
• Increased sleepiness
• Nervousness
• Tremor
• Unsteadiness

SKIN

• Dry, red skin

STOMACH AND INTESTINES

• Nausea
• Vomiting

Before Calling Emergency

Have this information ready:

• Person's age, weight, and condition (for example, is the person awake or alert?)
• Name of the product (ingredients and strength, if known)
• Time it was swallowed
• Amount swallowed
• If the medicine was prescribed for the person

Call for help even if you don't have this information.

Poison Control

Your local poison control center can be reached directly by calling the national toll-free Poison Help hotline (1-800-222-1222) from anywhere in the United States. This national hotline will let you talk to experts in poisoning. They will give you further instructions.

This is a free and confidential service. All local poison control centers in the United States use this national number. You should call if you have any questions about poisoning or poison prevention. It does NOT need to be an emergency. You can call for any reason, 24 hours a day, 7 days a week.

What to Expect at the Emergency Room

Take the container to the hospital with you, if possible.

The health care provider will measure and monitor the person's vital signs, including temperature, pulse, breathing rate, and blood pressure.

Tests that may done include:

• Blood and urine tests
• Chest x-ray
• Electrocardiogram (ECG)

Treatment may include:

• Fluids through a vein (by IV)
• Medicines to treat symptoms or reverse the effects of the overdose
• Activated charcoal
• Laxative
• Breathing support, including a tube through the mouth into the lungs and connected to a breathing machine (ventilator)

Outlook (Prognosis)

Recovery is likely if the person survives the first 24 hours. Complications such as pneumonia, muscle damage from lying on a hard surface for a long period of time, or brain damage from lack of oxygen may result in permanent disability.

Few people actually die from an antihistamine overdose. However, serious heart rhythm disturbances may occur, which can cause death.

Keep all medicines in child-proof bottles and out of reach of children.

References

Aronson JK. Anticholinergic drugs. In: Aronson JK, ed. Meyler's Side Effects of Drugs. 16th ed. Waltham, MA: Elsevier; 2016:534-539.

Eiwegger T, Simons FER, Akdis CA. Histamine and antihistamines. In: Burks AW, Holgate ST, O'Hehir RE, et al. eds. Middleton's Allergy: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2020: chap 92.

Hoppe JA, Monte AA. Anticholinergics. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 140.