To investigate the possible metabolic interaction between cannabidiol (CBD) and secobarbital, 6 male volunteers received 150 mg/70 kg sodium secobarbital orally immediately after smoking a marihuana cigarette prepared to deliver 0, 150, or 500 mug/kg CBD. The study was performed in a double-blind manner with each of the three treatments being assigned to every subject. Clinical effects and plasma secobarbital concentrations were recorded at periodic intervals. CBD did not alter the summary parameters which describe the secobarbital plasma concentration time curve. Secobarbital half-life, peak concentration, time of peak concentration, and area under the curve were unchanged by the coadministration of CBD. Clinical effects of secobarbital were also unaltered by CBD pretreatment. Thus at the doses administered, CBD does not appear to inhibit secobarbital metabolism in man.