Diphenhydramine Dosage Guide

## Can Diphenhydramine Kill You? Yes. Diphenhydramine overdose is a genuine medical emergency with a real mortality rate. This is not a theoretical risk -- emergency departments see diphenhydramine-related deaths, and it is one of the most common OTC drugs involved in intentional self-poisoning. ## Recognizing Overdose The progression of overdose typically follows this pattern: - **Mild toxicity (200-500 mg in adults)**: Tachycardia, dry mouth, blurred vision, urinary retention, agitation, confusion, mild hallucinations - **Moderate toxicity (500-1000 mg)**: Frank delirium with convincing hallucinations, heart rate above 130 bpm, fever, inability to urinate, significant QRS or QT changes on ECG - **Severe toxicity (1000+ mg)**: Seizures, wide-complex tachycardia, hyperthermia above 40C / 104F, rhabdomyolysis, coma, cardiac arrest The most dangerous feature of diphenhydramine overdose is that the person experiencing it may be too delirious to recognize they are in medical danger or to call for help. ## What to Do **If you are with someone who has taken a large dose of diphenhydramine:** - Call emergency services (911 in the US) immediately if the person shows signs of moderate or severe toxicity - Do not wait for symptoms to "get worse" -- the transition from delirium to cardiac arrhythmia can be sudden - Keep the person still and cool. Do not give them anything to eat or drink if they are severely confused - If they are seizing, clear the area around them but do not restrain them or put anything in their mouth - Tell emergency responders exactly what was taken, how much, and when **Medical treatment for diphenhydramine overdose** includes: - **Sodium bicarbonate** for QRS widening -- alkalinizing the blood overcomes sodium channel blockade, the same protocol used for tricyclic antidepressant overdose - **Benzodiazepines** for seizures and agitation - **Active cooling** for hyperthermia - **Physostigmine** -- a cholinesterase inhibitor that directly reverses anticholinergic delirium by increasing synaptic acetylcholine levels. It is used cautiously because it can cause bradycardia and bronchospasm, but it is the specific antidote - **Cardiac monitoring** -- continuous ECG monitoring is standard because arrhythmias can develop hours after ingestion - **IV fluids** and electrolyte monitoring, particularly if rhabdomyolysis is suspected ## After an Overdose Diphenhydramine overdose, particularly intentional overdose, is frequently associated with suicidal intent. Medical teams will typically initiate a psychiatric evaluation. If you or someone you know is struggling, the 988 Suicide and Crisis Lifeline (call or text 988 in the US) provides immediate support.