depressants, especially barbiturates. Although not commonly used, picrotoxin is effective as both a pesticide and a pediculicide. In the 19th century, it was used in the preparation of hard multum, which was added to beer to make it more intoxicating. This preparation has since been outlawed. Despite its potential toxicity to mammals in large enough doses, picrotoxin is also sometimes used as a performance enhancer in horses. It is classified as an illegal "Class I substance" by the American Quarter Horse Association. Substances that are classified as “Class I” are likely to affect performance and have no therapeutic use in equine medicine. In 2010, quarter horse trainer Robert Dimitt was suspended after his horse, Stoli Signature, tested positive for the substance. As with humans, it is used to counteract barbiturate poisoning. See also GABAA receptor negative allosteric modulator GABAA receptor § Ligands References Further reading GABAA receptor negative allosteric modulators GABAA-rho receptor negative allosteric modulators Glycine receptor antagonists Convulsants Lactones Epoxides Chloride channel blockers Neurotoxins Plant toxins