The blue-ringed octopus is the size of a golf ball, but its venom is powerful enough to kill humans. There is no known antidote.
The octopus produces venom that contains tetrodotoxin, 5-hydroxytryptamine, hyaluronidase, tyramine, histamine, tryptamine, octopamine, taurine, acetylcholine, and dopamine. The major neurotoxin component of blue-ringed octopus venom was originally known as maculotoxin, but was later found to be identical to tetrodotoxin, a neurotoxin which is also found in pufferfish and cone snails. Tetrodotoxin blocks sodium channels, causing motor paralysis and sometimes respiratory arrest leading to cardiac arrest due to a lack of oxygen. The toxin is created by bacteria in the salivary glands of the octopus.
First aid treatment is pressure on the wound and rescue breathing. It is essential, if rescue breathing is required, that it be continued until the victim begins to breathe, which may be some hours. Hospital treatment involves respiratory assistance until the toxin is washed out of the body. The symptoms vary in severity, with children being the most at risk because of their small body size. The victim might be saved if artificial respiration starts before marked cyanosis and hypotension develop. Victims who live through the first 24 hours generally go on to make a complete recovery.
It is essential that immediate and full time respiratory support be given (e.g. artificial respiration/rescue breathing) even if the victim appears not to be responding. Tetrodotoxin poisoning can result in the victim being fully aware of his/her surroundings but unable to breathe. Because of the paralysis that occurs they have no way of signalling for help or any way of indicating distress. Respiratory support, together with reassurance, until medical assistance arrives ensures that the victim will generally recover well.
The blue-ringed octopus is currently one of the most toxic known sea creatures. Another cephalopod, Pfeffer's Flamboyant Cuttlefish, produces a venom roughly equal in potency to that of the blue-ringed octopus. Despite its small size, the blue-ringed octopus carries enough poison to kill 26 adult humans within minutes.