SR-17018

SR-17018, also known informally as SR-17 or just SR and as 5,6-dichloro-desmethylchlorphine, is an atypical opioid receptor modulator with unusual actions and effects. It acts as a biased partial agonist of the μ-opioid receptor (MOR), showing strong selectivity for activation of G protein signaling over β-arrestin2 recruitment at this receptor. In addition, the drug appears to also act as a MOR positive allosteric modulator, with this possibly being its primary action. Unlike conventional opioids such as morphine and fentanyl, SR-17018 produces robust analgesic effects in rodents with very little respiratory depression and with much less analgesic tolerance. Moreover, substitution of conventional opioids like morphine with SR-17018 can reverse analgesic tolerance and suppress withdrawal symptoms in rodents. However, conflicting findings exist in terms of analgesic tolerance and respiratory depression. The drug has not been formally studied in humans. SR-17018 was first described in the scientific literature by Laura Bohn and colleagues in 2017. It was encountered online as a novel designer drug by 2023. Subsequently, discussion of SR-17018 on the social media website Reddit dramatically increased in 2024. Although technically a designer opioid, SR-17018 is said to have very different effects from other opioids, for instance producing minimal euphoria. Rather than being used recreationally itself, SR-17018 is typically employed by users to prevent opioid withdrawal symptoms and facilitate opioid discontinuation in the context of opioid dependence. Nonetheless, in July 2026, the Drug Enforcement Administration (DEA) announced its intention to temporarily make SR-17018 a Schedule I controlled substance in the United States under emergency scheduling protocols, with this announcement receiving opposition.