Can You Overdose On Benadryl (Diphenhydramine)? What Are The Symptoms?

Answer

Like any drug or medication, it is possible to overdose on Benadryl (diphenhydramine) if you take doses exceeding the recommended amount.

In the sections below, I discuss the available information regarding Benadryl overdose, including statistics from Poison Control, symptoms of an overdose, and what to do if you think you have taken too much, but, I want to start off by providing information on available resources if you think you have overdosed or you are thinking of doing it purposefully.

• Poison Control Center: (1-800-222-1222)
• National Suicide Prevention Lifeline: 1-800-273-8255

I also want to say at the beginning here that taking two tablets of Benadryl (which you state in your question) is still within the normal dosage range for adults (which is 25-50mg per dose). Each tablet of Benadryl contains 25mg of diphenhydramine, so there is little concern about taking two tablets.

What Is Benadryl?

Benadryl is a common over-the-counter antihistamine used for the treatment of allergies, nausea, and insomnia (trouble sleeping). It is available in many different dosage forms (e.g. capsules, tablets, liquid gels, etc...) and is used in a variety of over-the-counter cough/cold products.

While Benadryl is an effective antihistamine, it is commonly included in a variety of over-the-counter products as a sleep aid, due to its sedating properties.

Antihistamine Overdose

Whether intentional or not, overdosing on antihistamines, which includes Benadryl, are among the most commonly reported drug classes responsible for an overdose as reported by Poison Control Centers in the United States. In 2002 alone, over 23,000 reports were from antihistamines.

• Of those overdose reports in 2002, 5 were fatal in regard to Benadryl overdose alone.

In 2003, reports of Benadryl overdoses exceed 28,000! As these numbers are extremely high, it is important to know the symptoms of a potential Benadryl overdose.

Common Symptoms Of A Benadryl Overdose

• Cardiac dysrhythmias
• Seizure activity
• Pupil Dilation
• Nausea/Vomiting
• Extreme lethargy
• Respiratory failure
• Agitation
• Hallucinations

It should be noted that when taken within normal dosing guidelines, Benadryl is a safe and effective drug with a large therapeutic window, meaning that it takes excessive dosages to experience severe symptoms of overdose.

There are various guidelines and reports regarding just how much Benadryl is considered an overdose. One study reported certain dosage levels that correlated with symptom onset, which is described below.

Doses At Which Moderate Symptoms Of Benadryl Overdose Occur

• Moderate symptoms (e.g. nausea, agitation, confusion, cardiac changes) of overdose most often begin at dosages of 300 mg (12 adult strength tablets).

Doses At Which Severe Symptoms Of Benadryl Overdose Occur

• Severe symptoms are most often seen at dosages over 1,000 mg (40 adult strength tablets). These symptoms include delirium, seizures, and coma.

What Is Considered An Overdose For Benadryl?

It is well known that Benadryl has dose-dependent toxic effects but the exact dosages at which toxicity develops aren't well known. Although we detailed above common dosages that correlated with adverse events, it is important to know when an overdose is considered to have occurred. 

The recommended adult dose for Benadryl is 25mg to 50mg every four to six hours, so, technically, anything over 50mg (two tablets) would be considered an overdose. Nevertheless, a variety of studies classify an 'overdose' as a dose that should be reported to Poison Control, which is generally in the 200-300mg range. 

One guideline gives an approximate dosage of Benadryl that is considered excessive and should be reported to a Poison Control Center. These levels are discussed below.

Benadryl Overdose: Children Less Than 6 Years Of Age

An overdose of Benadryl is considered to have occurred in those who ingest at least 7.5 mg per kilogram of body weight. An example dosage for a 30-pound child would be around 100 mg of Benadryl (4 adult strength tablets or 8 teaspoons of children's 12.5 mg/ml liquid).

Benadryl Overdose: Patients 6 Years Of Age And Older

An overdose is considered to have occurred in those who ingest at least 7.5 mg per kilogram of body weight or 300 mg of Benadryl (12 adult strength tablets), whichever is less.

Additional Information

• Variation among individuals (e.g. age, weight, metabolic factors)

• Co-administration of other drugs

• Concomitant disease states

• Supportive care

Final Words

The following is important to reiterate.

If you feel you have taken too much Benadryl or are having symptoms after taking it, it is important to call the Poison Control Center (1-800-222-1222) immediately. In addition, you should immediately go to the hospital if an overdose is thought to have occurred for supportive care.

Lastly, if you or someone you know has talked about overdosing on Benadryl, or any medication, know that help is available. You can call the National Suicide Prevention Lifeline at 1-800-273-8255.

I hope this answer helped! Thanks so much for reaching out.