Which of the following is a likely symptom of anticholinergic poisoning? Recognizing the Anticholinergic Toxidrome

October 10, 2025 •

3 min read

According to the well-known medical mnemonic, one of the classic signs of anticholinergic poisoning is to be “blind as a bat” due to dilated pupils and blurred vision. Recognizing which of the following is a likely symptom of anticholinergic poisoning is a critical skill for both healthcare professionals and caregivers, as timely diagnosis is key to effective treatment.

Quick Summary

Anticholinergic poisoning, or anticholinergic toxidrome, is a medical emergency caused by an excess of anticholinergic substances. It presents with characteristic symptoms including dilated pupils, dry mouth and skin, flushed appearance, hyperthermia, and altered mental status.

Key Points

Classic Mnemonic: Symptoms can be remembered by 'red as a beet, dry as a bone, blind as a bat, mad as a hatter, hot as a hare, and full as a flask'.
Altered Mental Status: Key central symptoms include confusion, delirium, and hallucinations.
Hyperthermia and Dry Skin: A defining feature is high body temperature and lack of sweating.
Dilated Pupils: Dilated pupils (mydriasis) causing blurred vision are characteristic peripheral signs.
Tachycardia: An increased heart rate is a common cardiovascular effect.
Common Causes: Include overdose of certain antihistamines, tricyclic antidepressants, and plants like Jimson weed.
Prompt Treatment: Early recognition and supportive care are critical. Physostigmine can be used for severe central effects, with caution.

What is Anticholinergic Poisoning?

Anticholinergic poisoning, also known as anticholinergic toxidrome, occurs when there is an overabundance of anticholinergic substances in the body. These substances compete with and block the action of acetylcholine, a key neurotransmitter in both the central and peripheral nervous systems. Acetylcholine is responsible for a variety of bodily functions, including regulating heart rate, muscle movement, glandular secretions, and cognitive processes. By blocking acetylcholine's effects, anticholinergic agents lead to a distinct set of symptoms that can range from mild to life-threatening. Recognition of these symptoms is crucial for prompt medical intervention.

The Classic Mnemonic: 'Red as a Beet...'

A traditional mnemonic used in medicine effectively summarizes the characteristic symptoms of anticholinergic poisoning. It's a memorable tool for rapid assessment of the toxidrome:

'Red as a beet': Refers to flushed skin.
'Dry as a bone': Indicates dry skin and mucous membranes.
'Blind as a bat': Describes dilated pupils (mydriasis) and blurred vision.
'Mad as a hatter': Points to altered mental status, confusion, delirium, and hallucinations.
'Hot as a hare': Refers to hyperthermia.
'Full as a flask': Signifies urinary retention.

Detailing the Symptoms: Central vs. Peripheral Effects

Anticholinergic poisoning affects both the brain (central nervous system) and the body's involuntary functions (peripheral nervous system). The severity depends on the dose and substance.

Central Nervous System (CNS) Symptoms

Effects in the brain include:

Altered Mental Status: Confusion, disorientation, or agitation.
Delirium and Hallucinations: May include visual or tactile hallucinations.
Seizures and Coma: Possible in severe cases.
Memory Impairment: Often accompanies confusion.

Peripheral Nervous System Symptoms

Effects on the body include:

Cardiovascular Effects: Tachycardia is common. Severe toxicity can cause arrhythmias.
Thermoregulatory Issues: Hyperthermia and dry skin.
Gastrointestinal Effects: Decreased gut motility, reduced bowel sounds, constipation, or functional ileus.
Genitourinary Issues: Difficulty urinating or urinary retention.
Ocular Effects: Dilated pupils causing blurred vision and light sensitivity.

What Causes Anticholinergic Poisoning?

Sources include medications and plants. Overdose or additive effects of multiple medications (polypharmacy) are common, especially in older adults.

Common Medication Sources

Antihistamines: First-generation ones like diphenhydramine.
Tricyclic Antidepressants (TCAs): Amitriptyline, doxepin.
Antipsychotics: Some older and newer drugs.
Anti-Parkinsonian Medications: Benztropine, trihexyphenidyl.
Muscle Relaxants: Cyclobenzaprine.
Overactive Bladder Medications: Oxybutynin, tolterodine.

Common Plant Sources

Jimson Weed (Datura stramonium): Contains tropane alkaloids.
Deadly Nightshade (Atropa belladonna): Contains toxic alkaloids.

How Is Anticholinergic Poisoning Treated?

Treatment involves supportive care and symptom management.

Stabilizing Vital Signs: Airway, breathing, and circulation are priorities.
Decontamination: Activated charcoal within one hour if appropriate.
Supportive Care: Cooling for hyperthermia, benzodiazepines for agitation/seizures.
Antidote Administration: Physostigmine can be used for severe central effects like delirium or hallucinations. It's an acetylcholinesterase inhibitor that increases acetylcholine. Caution is needed with cardiac conditions or TCA poisoning.

Comparison: Anticholinergic vs. Cholinergic Poisoning

Comparing anticholinergic and cholinergic effects aids diagnosis. Anticholinergic poisoning blocks acetylcholine, while cholinergic poisoning overstimulates it.


Symptom	Anticholinergic Poisoning (Blocks Acetylcholine)	Cholinergic Poisoning (Excess Acetylcholine)
Mental Status	Altered mental status, delirium, agitation	Altered mental status, weakness, seizures
Pupils	Dilated (Mydriasis), non-reactive to light	Constricted (Miosis)
Sweating	Decreased or absent (Dry skin)	Increased sweating (Diaphoresis)
Skin	Hot, red, flushed, dry	Cold, clammy, wet
Heart Rate	Increased (Tachycardia)	Decreased (Bradycardia)
Secretions	Decreased saliva, mucus, and tears (Dry mouth)	Increased secretions (Salivation, lacrimation)
Bowel Sounds	Decreased or absent	Increased
Urinary Function	Urinary retention	Urinary incontinence

Conclusion: The Importance of Recognition

Anticholinergic poisoning presents with a clear set of symptoms affecting the central and peripheral nervous systems. Early recognition is crucial, especially in vulnerable populations like the elderly on multiple medications and children who may ingest plants. This enables timely supportive care and, if needed, antidotal therapy for the best outcome. More information can be found in the {Link: Medscape article https://emedicine.medscape.com/article/812644-clinical} and {Link: StatPearls article https://www.ncbi.nlm.nih.gov/books/NBK534798/}.

Frequently Asked Questions

The classic mnemonic is 'red as a beet, dry as a bone, blind as a bat, mad as a hatter, hot as a hare, and full as a flask'.

Central anticholinergic poisoning can cause agitated delirium, confusion, and visual hallucinations.

Medications with first-generation antihistamines, like diphenhydramine, commonly found in cold and sleep aids, can cause toxicity.

Diagnosis is based on observing characteristic signs and symptoms and a history of exposure to an anticholinergic substance.

Anticholinergic poisoning blocks acetylcholine, causing 'dry' symptoms, while cholinergic poisoning involves excess acetylcholine, causing 'wet' symptoms.

Sources include overdoses of prescription drugs (e.g., TCAs, antipsychotics), OTC medications (e.g., antihistamines), and toxic plants (e.g., Jimson weed, deadly nightshade).

No. While effective for severe central effects, physostigmine is used cautiously and may be contraindicated with certain cardiac conditions or TCA overdose.