Chlorpyrifos, commonly sold under the trade name Dursban, was until recently one of the most widely used pesticides in the United States. The loose form of this organophosphate insecticide, which is related to nerve gas, was pulled from the residential market in 2000 after it was linked to asthma and reproductive problems, among other issues. (It's still used in contained bait traps.) Chlorpyrifos can send the nervous system into overdrive, leading to nausea, dizziness, confusion, and, at high exposures, respiratory paralysis and death. Though it is no longer sold to consumers, Dursban and its ilk are still allowed for commercial agricultural use in the U.S., and are sold overseas.