A clinical trial tested whether cannabidiol (CBD) can reduce the adverse effects of tetrahydrocannabinol (THC) and improve its tolerability as an analgesic. Healthy volunteers received THC alone or with different doses of CBD. Contrary to expectations, the highest CBD dose (450 mg) significantly increased THC's subjective, psychomotor, cognitive, and autonomous effects—for example, feeling high increased by 60.5%—and did not enhance pain relief. Lower CBD doses had no significant effect on THC's effects. CBD also increased blood levels of THC and its active metabolite. The findings do not support using CBD to reduce oral THC's adverse effects or to improve its analgesic properties.
A single intravenous dose of S-ketamine produced acute and delayed effects on brain activity and motor cortex excitability that lasted up to seven days in 16 healthy adults. Intravenous S-ketamine reduced motor-evoked potential amplitude acutely and caused a sustained weakening of long-interval intracortical inhibition, which followed a linear relationship with drug concentration. Transcranial magnetic stimulation combined with electroencephalography showed acute changes in brain electrical activity across all treatments, but delayed changes only after intravenous and high-dose oral S-ketamine. Electroencephalography revealed acute decreases in alpha, beta, and delta power with eyes closed, and sustained increases in delta power with eyes open, the latter also showing a linear concentration-effect relationship. These delayed pharmacodynamic effects are distinct from acute effects and may help explain S-ketamine's antidepressant action.