Mad honey poisoning, or mad honey intoxication, is a condition of intoxication caused by consumption of honey containing grayanotoxin. Grayanotoxin can be isolated from plants of the Ericaceae family (including Rhododendron, Kalmia, Agarista, and Pieris), and intoxication can occur through consumption of leaves or flowers of these plants or products derived from these plants such as honey (known as mad honey), teas, or alternative medicine formulations. Although intoxication with grayanotoxin is generally accidental, several grayanotoxin-containing honey preparations are now sold online and used for purported health benefits. Contamination of honey with grayanotoxin occurs most commonly in Turkey, along the eastern coast of the Black Sea, from Rhododendron-derived honey.

Grayanotoxin binds to a subunit of intracellular sodium channels found on neurons and cardiac muscle. Symptoms are thought to be related to sodium channel activation and vagal nerve stimulation.

The signs and symptoms of grayanotoxin intoxication vary depending primarily on the quantity of toxin ingested and the concentration of the toxin in the honey consumed. Common findings include cardiac rhythm disorders (sinus bradycardia and various degrees of heart block culminating in asystole is severe intoxication), nausea and vomiting, diarrhea, hypotension, blurred vision, diaphoresis, altered mental status, and dizziness. Symptoms develop 20 minutes to 3 hours after ingestion and can last for up to 48 hours. The intoxication is seen most commonly in men aged 50-60 years. Chronic consumption of mad honey can results in a syndrome of sinus bradycardia, first- or second-degree heart block, and presyncope.