Salvinorin A, the active component of the hallucinogenic plant Salvia divinorum, produces pain relief (antinociception) and lowers body temperature in mice by activating the kappa-opioid receptor. These effects were observed after injection of salvinorin A or a similar compound, salvinorinyl-2-propionate, into the brain of normal mice, but not in mice genetically lacking the kappa-opioid receptor. Salvinorin A showed high affinity specifically for the kappa-1 subclass of opioid receptors. In contrast, salvinorin B, an inactive derivative, had no effect on pain or body temperature. The findings confirm that salvinorin A acts through the kappa-opioid receptor to produce its behavioral effects.
A new class of iboga alkaloids, called oxa-iboga, was created by modifying the iboga molecular structure to replace a key component with a benzofuran ring. These compounds lack the heart rhythm risks (proarrhythmic effects) of ibogaine and noribogaine when tested on human heart cells. In male rats, oxa-iboga compounds were more effective than ibogaine at reducing opioid use. They act as potent kappa opioid receptor agonists but produce different behavioral effects than typical kappa agonists. A single dose or short treatment with oxa-noribogaine led to long-lasting reductions in morphine, heroin, and fentanyl intake, reversed persistent opioid-induced pain sensitivity, and suppressed drug-seeking behavior in relapse models. These compounds offer a mechanistically distinct approach to treating opioid use disorder.