Antihistamine Overdose: Types, Symptoms, And Treatment - Healthline

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Is It Possible to Overdose on Antihistamines?

Medically reviewed by Dena Westphalen, PharmD — Written by Valencia Higuera on February 11, 2019

Overview
Types
Symptoms
Treatment
Seeking medical help
Safety information
Usage for children
Summary

An antihistamine overdose, also called antihistamine poisoning, occurs when there’s too much of the medication in your body. This can be life-threatening.

Can you take too much allergy medication?

Antihistamines, or allergy pills, are medications that reduce or block the effects of histamine, a chemical the body produces in response to an allergen.

Whether you have seasonal allergies, indoor allergies, pet allergies, food allergies, or a chemical sensitivity, an allergic response can trigger multiple symptoms, such as:

sneezing
coughing
sore throat
runny nose
skin rash
ear congestion
red, itchy, watery eyes

Allergy medication is considered safe when used correctly and can provide quick relief from symptoms, but it’s possible to take too much. It’s important that you understand proper dosing to avoid toxicity.

Types of antihistamines

Antihistamines include first-generation medications that have a sedating effect and newer non-sedating types.

Examples of sedating antihistamines include:

cyproheptadine (Periactin)
dexchlorpheniramine (Polaramine)
diphenhydramine (Benadryl)
doxylamine (Unisom)
pheniramine (Avil)
brompheniramine (Dimetapp)

Examples of non-sedating antihistamines include:

loratadine (Claritin)
cetirizine (Zyrtec)
fexofenadine (Allegra)

Symptoms of antihistamine overdose

It’s possible to overdose on both types of antihistamines. Symptoms of an overdose when taking sedating medication can vary but may include:

increased drowsiness
blurred vision
nausea
vomiting
increased heart rate
confusion
loss of balance

More serious complications of first-generation antihistamine overdose include seizures and coma.

Non-sedating antihistamine overdoses tend to be less toxic and less severe. Symptoms may include:

dizziness
headache
drowsiness
agitation

Sometimes, however, tachycardia can occur. This is when your resting heart rate is more than 100 beats per minute.

Symptoms of an overdose usually appear within six hours of taking too much antihistamine. Your symptoms may start off mild and then gradually worsen over time.

Deaths from antihistamine overdose

There have been reports of death due to antihistamine toxicity. These include accidental overdoses and intentional misuse.

Death can occur when an overdose causes severe complications such as respiratory distress, cardiac arrest, or seizures. Each person’s tolerance to medication can vary. However, toxicity usually occurs when a person ingests three to five times the recommended dosage.

Medical emergency
To avoid life-threatening complications, call 911 or go to the emergency room if you have any symptom of an overdose. You can also call the Poison Control Help Line at 800-222-1222.

Antihistamine overdose treatment

Antihistamine overdose treatment focuses on stabilizing your health and providing supportive care.

You’ll likely receive activated charcoal in the hospital. This product is used in emergency situations to help reverse the effects of poisoning. It works as an antidote, stopping the absorption of toxins and chemicals from your stomach into the body. Toxins then bind to the charcoal and exit the body through bowel movements.

In addition to activated charcoal, general support may include cardiac and respiratory monitoring.

The prognosis depends on the amount of antihistamine ingested and the extent of an overdose, but a full recovery is possible with immediate medical treatment.

When to see a doctor

Some side effects of taking antihistamines can mimic symptoms of an overdose. These include mild nausea, dizziness, vomiting, diarrhea, and stomach pain.

These symptoms don’t usually require medical treatment, and may subside as your body adjusts to the medication. Even so, check with a doctor if you have side effects. You may need to reduce your dosage or take a different medication.

The difference between a side effect and an overdose is the severity of symptoms. Severe symptoms like rapid heart rate, tightness in the chest, or convulsions require a visit to the emergency room.

How to use antihistamines safely

Antihistamines are safe when used properly. Here are some tips to avoid ingesting too much:

Don’t take two different types of antihistamines simultaneously.
Don’t take more than the recommended dosage.
Don’t double up on doses.
Keep drugs out of reach of children.
Don’t take two doses too close together.

Make sure you read labels carefully. Some antihistamines can interact with other drugs you take. If you don’t know whether it’s safe to combine an antihistamine with another medication, speak with a doctor or pharmacist.

Be mindful that some antihistamines include other ingredients like a decongestant. If you take these types of antihistamines, it’s important that you don’t take a separate decongestant.

Antihistamines and children

Antihistamines can also relieve allergy symptoms in children, but they aren’t right for all children. Generally speaking, you shouldn’t give an antihistamine to a child under the age of 2.

Dosage recommendations for children ages 2 and up vary depending on the type of antihistamine, and it’s sometimes based on a child’s weight.

Talk to your child’s pediatrician or pharmacist if you have questions about the proper dosage.

Takeaway

Whether you have seasonal or indoor allergies, an antihistamine can help relieve symptoms like sneezing, a runny nose, sore throat, and watery eyes.

However, taking too much of an antihistamine can lead to an overdose or poisoning. Be sure to read medicine labels carefully and don’t take more than directed.

How we reviewed this article:

SourcesHistoryHealthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Activated charcoal - activated charcoal suspension. (2018). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7da3506f-2799-434c-e053-2a91aa0adabb
Antihistamine poisoning. (2017).https://www.rch.org.au/clinicalguide/guideline_index/Antihistamine_poisoning/
Borowy C. (2018). Antihistamine toxicity.https://www.ncbi.nlm.nih.gov/books/NBK482318/
Jensen LL, et al. (2016). A Danish survey of antihistamine use and poisoning patterns. DOI:https://onlinelibrary.wiley.com/doi/pdf/10.1111/bcpt.12632
Manning B. (n.d.). Chapter 18: Antihistamines. Poisoning and drug overdose. https://accessmedicine.mhmedical.com/content.aspx?sectionid=42069832&bookid=391
MekonnenS. (n.d.). Antihistamine: Using them safely.https://www.poison.org/articles/2012-jun/antihistamines-using-them-safely
Thomas SHL. (2016). Antihistamine poisoning. DOI: https://doi.org/10.1016/j.mpmed.2015.12.002
Use caution when giving cough and cold products to kids. (2018). https://www.fda.gov/drugs/resourcesforyou/specialfeatures/ucm263948.htm

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Medically reviewed by Dena Westphalen, PharmD — Written by Valencia Higuera on February 11, 2019

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Antihistamine overdose treatment

When to see a doctor

How to use antihistamines safely

Antihistamines and children

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