Opioids in the Frame of New Psychoactive Substances Network: A Complex Pharmacological and Toxicological Issue

Background: New psychoactive substances (NPS), often referred to as "legal highs" or "designer drugs", are derivatives and analogues of existing psychoactive drugs that are introduced in the recreational market to circumvent existing legislation on drugs of abuse. Objective: This systematic review aims to gather the state of the art regarding chemical, molecular pharmacology and toxicological information of opioid class of NPS. Methods: Chemical, pharmacological, toxicological and clinical effects of opioid class of NPS were searched in books and in PubMed (U.S. National Library of Medicine) without a limiting period. Results: Within this class, fentanyl analogues are among the most frequently abused and pose several clinical concerns and therefore will be thoroughly discussed. Other opioid sub-categories of NPS frequently misused include AH-7921, MT-45, U-47700, U-50488, desomorphine, mitragynine, tramadol, tapentadol, salvinorin A and its analogue herkinorin. Conclusion: Due to inefficient monitoring techniques, as well as limited knowledge regarding the acute and long-term effects of opioids NPS, further clinical and forensic toxicological studies are required.