1-(4-Nitrophenylethyl)piperidylidene-2-(4-chlorophenyl)sulfonamide

Overview
1-(4-Nitrophenylethyl)piperidylidene-2-(4-chlorophenyl)sulfonamide (W-18) is a potent μ-opioid agonist with a distinctive chemical structure which is not closely related to other established families of opioid drugs. It was invented by the chemists Edward Knaus, Brent Warran and Theodore Ondrus in 1981.

This compound was found to be around 10,000x more potent than morphine in animal studies, however due to its structural differences from other opioid drugs it would be difficult to represent as being "substantially similar in chemical structure" to any controlled drugs. This makes it likely that it would be legal throughout the world.

It has never been used in humans, but would be expected to produce effects similar to those of other potent opioid agonists, including strong analgesia, sedation, euphoria, constipation, itching and respiratory depression which could be harmful or fatal. Tolerance and dependence would be expected to develop rapidly based on the potency of the drug, as it is of a similar strength to carfentanil and so would most likely cause pronounced tachyphylaxis following repeated dosing, as is seen with the potent fentanyl analogues.