Fugu contains lethal amounts of the poison tetrodotoxin in the organs, especially the liver area and ovaries, and also the skin. The poison, a sodium channel blocker, paralyzes the muscles while the victim stays fully conscious, and eventually dies from asphyxiation. Currently, there is no known antidote, and the standard medical approach is to try to support the respiratory and circulatory system until the poison dissipates.

As of 2008, advances in fugu research and farming have allowed some farmers to mass produce non-toxic fugu. Researchers surmised that fugu's tetrodotoxin came from eating other animals that had the tetrodotoxin-laden bacteria, and developed immunity over time. Many farmers now are producing 'poison-free' fugu by keeping the fugu away from tetrodotoxin-laden bacteria. Usuki, a town in ÅŒita Prefecture, became famous for selling non-poisonous fugu. No one has been poisoned eating it yet.[1]