Preclinical Evidence for a Drug–Drug Interaction Between Cannabinol and Melatonin

The worldwide legalization of medicinal cannabis has led to an increased use of products made by commercial operators. These products often contain minor cannabinoids such as cannabinol (CBN) which are advertised to improve sleep. Products are also available in which CBN is combined with conventional therapies, with a common product containing both CBN and the widely used sleep-aid melatonin. The combination of CBN and melatonin provides potential for a pharmacokinetic drug–drug interaction (DDI) given that cannabinoids are known to inhibit drug-metabolizing enzymes. Indeed, we recently reported that CBN potently inhibited the CYP1A2-mediated metabolism of caffeine. CYP1A2 is the major hepatic enzyme involved in the metabolism of melatonin; thus, in this study, we aimed to examine whether CBN inhibited CYP1A2-mediated metabolism of melatonin in vitro and in vivo. We found CBN potently inhibited CYP1A2-mediated metabolism of melatonin and increased the apparent oral bioavailability of melatonin in mice with a four-fold increase in the plasma melatonin exposure. Our results provide an additional example of a potential DDI involving melatonin.