The level of toxicity is seasonal, and, in Japan, fugu is served only from October through March. Tetrodotoxin blocks 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 the action potential blockade. 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 each year from tetrodotoxin poisoning in Japan.
Recovery takes days to occur.
No known racial predilection exists. However, the poisoning is more common in Japanese because of their dietary preferences for fugu. The first symptoms occur 15 minutes to several hours postingestion 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.