DB09173 (Butyrfentanyl or butyrylfentanyl) is a potent, short-acting mu opioid receptor agonist, and an analog of fentanyl, differing by only one methyl group. It has no approved medical indications but is being used for recreational purposes, with cases of fatal overdoses reported in Europe and the United States. Pre-clinical studies of butyrfentanyl are scarce; however, the few available studies suggest that butyrfentanyl is about 30 times less potent than fentanyl itself, and has significant antinociceptive properties, as demonstrated by the acetic acid writhing test in rodents. DB09173 is being abused for its opioid effects. As with other mu-opioid agonists, it can induce respiratory depression which may lead to death and numerous deaths have been reported. No studies of butyrfentanyl dependence or cross-dependence conducted in humans could be identified.

AH-7921 (3,4-Dichloro-N-([1-(dimethylamino)cyclohexyl] methyl)benzamide) is an N-substituted cyclohexylmethylbenzamide classified as an opioid analgesic with high addictive liability. The compound acts as an agonist of μ-opioid receptors, although at high doses it can also stimulate κ-opioid receptors. In animal studies, AH-7921 produced typical morphine-like actions, i.e., antinociception, respiratory depression, sedation, miosis, inhibition of gut propulsion, and lowered body temperature, with a potency almost equipotent to that of morphine. There is limited information available on the routes of administration and the doses of AH-7921 used. The compound is taken orally, nasally, by smoking, and, less commonly, by intravenous injection. Minimal oral effective doses for complete pain suppression by AH 7921 are 1.25 and 13.8 mg/kg for canine and rhesus monkey, respectively.