Pure opioid agonists such as Morphine, Hydromorphone, and Fentanyl stimulate opioid receptors and are the most potent analgesics. Fentanyl and fentanyl analogues are up to 100 times more powerful than morphine and 30-50 times more powerful than heroin.

Fentanyl abuse is causing significant problems worldwide. In the U.S., age-adjusted rate of death involving Fentanyl has increased 80% in 2014.

Sources include production in illicit clandestine labs or diversion from legitimate pharmaceutical sales.

12 different analogues of Fentanyl have been identified in the U.S. drug traffic market.

Commonly laced in heroin or cocaine or sold as fake Oxycodone or OxyContin tablets.

W-18 is a highly potent opioid agonist with a distinctive chemical structure which is not closely related to older established families of opioid drugs. While Fentanyl is approximately 100 times more powerful than Morphine, W-18 is about 100 times more powerful than Fentanyl.

First discovered at the University of Alberta in 1982 in hopes of producing a non-addictive analgesic, 32 compound series named from W-1 to W-32, with W-18 being the most potent.

Recently emerged on the streets of Canada when police in Calgary confiscated 110 green pills being sold as Fentanyl, known on the streets as "shady eighties" or "green beans pills" but chemical analysis revealed some pills containing W-18 instead.

W-18 has never been used clinically as drug companies did not pick the patent, which lapsed by 1992 so little clinical experience.

The effects of naloxone to reverse this synthetic opioid are unknown and higher doses are expected to to be required.

Illicit drug manufacturers research pharmacological history in search of the more powerful, exotic, and new opioids to circumvent current legal regulations.

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