It was a naturally occurring and highly potent neurotoxin found in the puffer fish and the Japanese fugu. Its method of operation was to block nerve signals by interfering with the sodium process through cells. Symptoms of tetrodotoxin poisoning included pulmonary oedema, hypotension, cyanosis, hypothermia, respiratory distress, paralysis and death.
Justine Wheaton took a pill that combined tetrodotoxin and an amphetamine derivative. As part of the Seventh Doctor's plan to defeat the Butler Institute, she would appear dead, be taken to the Institute, and awake to let the Doctor, Ace, and others into the building. (PROSE: Cat's Cradle: Warhead)
In Haiti, its sacramental use was central to the zombie phenomenon. It lowered people's senses and put them in hypnotic states; they would be buried, dug up later, and be tricked into thinking they had died and were subsequently turned into slaves. It was similar to another drug used by Usurians to maintain the slaves on their business planets. (PROSE: White Darkness)