Saxitoxin poisoning, also known as paralytic shellfish poisoning, is caused by ingestion of shellfish contaminated with saxitoxin from dinoflagellate species in the genus Alexandrium. Numbness of the oral mucosa begins within hours of ingestion. This may be followed by nausea, vomiting, more generalized paresthesias, and muscle weakness that may progress to paralysis and, in severe cases, even death from respiratory failure.

Patients most often present in coastal locations, particularly in the Pacific Northwest and the Northeast United States. Commercially harvested shellfish is routinely tested for saxitoxin, and thus patients have typically ingested clams or mussels collected personally from local beaches.

Saxitoxin has been identified as a potential agent of bioterrorism, although it has not been used in an attack to date.