W-18 is a compound in a series of 32 substances (named W-1 to W-32) that were first synthesized in academic research on analgesicdrug discovery in the 1980s and appeared as a designer drug in the 2010s.
W-18 was commonly reported to be an opioid in the popular press in the 2010s, which was later revealed not to be correct.[7][8][9] W-18 was found to obtain weak activity at both sigma receptors and the translocator protein (peripheral benzodiazepine receptor).[9] It also inhibits the hERG potassium channel with micromolar affinity, which could potentially cause cardiac arrhythmia at high doses.[10]
In Sweden, W-18 was made illegal in January 2016.[11]
In Canada, W-18 and its analogues were made Schedule I controlled substances.[12] Possession without legal authority can result in maximum 7 years imprisonment. Further, Health Canada amended the Food and Drug Regulations in May, 2016 to classify W-18 as a restricted drug. Only those with a law enforcement agency, person with an exemption permit or institutions with Minister's authorization may possess the drug.