The level of toxicity is seasonal, and in Japan, fugu is only served from October through March. Tetrodotoxin acts to block diffusion of sodium through the sodium channel, preventing depolarization and propagation of action potentials in nerve cells. All of the observed toxicity is secondary to this blockade of the action potential. Tetrodotoxin also stimulates the chemoreceptor trigger zone in the medulla oblongata and depresses the respiratory and vasomotor centers in that area. Estimates vary, but up to 50 deaths may occur per year from tetrodotoxin poisoning in Japan.
Recovery occurs over a period of days.
No known racial predilection exists. However, the poisoning is more common in Japanese due to their dietary preferences for fugu. The first symptoms occur 15 minutes to several hours after ingestion of tetrodotoxin-containing food. Initial symptoms include lip and tongue paresthesias, followed by facial and extremity paresthesias and numbness. Salivation, nausea, vomiting, and diarrhea with abdominal pain develop early and can be severe.