For a long time, the cannabis community at large has propagated what may be a half-truth, that THC and CBD are a match made in heaven. In other words, CBD is the antidote to the negative effects of THC. When you throw in the controversial “entourage effect,” you even get an amplification of the best of both compounds. That’s why the market has experienced an upsurge of THC/CBD combinations as cannabinoid isolates have been forced to fade out.
John Hopkins Study: CBD Amplifies The Adverse Effects of THC
A recently published study has contradicted the popular belief that CBD is a good addition to the psychoactive cannabinoid THC. Researchers from John Hopkins University conducted a randomized clinical trial comparing the effects of THC + placebo and THC + CBD. The cannabinoids were offered in the form of infused brownies: 20 mg Δ9-THC + 640 mg CBD and 20 mg Δ9-THC + placebo.
The CBD group experienced more significant adverse effects in terms of feeling sick, red/dry eyes, increased heart rate, and impairment of cognitive and psychomotor ability.
What caused this effect? The scientists explained that CBD inhibited the metabolism (pharmacokinetics) of Δ9-THC and 11-OH-Δ9-THC hence increasing their plasma levels relative to the placebo group. This potentiated the adverse effects of THC, acutely.
The study can be accessed through JAMA Network Open Network here. The study was partly funded by the National Institute on Drug Abuse (NIDA).
Note: In this study, like in many others, a very very large dose of CBD was given (640 mg a day), much higher than most patients will ever consider taking.
What have other studies found about THC/CBD combinations?
A 2019 systematic review involving 16 studies with a total of 466 participants found that CBD blunts some of the adverse effects of THC. Some sources have also suggested that CBD (as a negative allosteric modulator of the CB1 receptors) offsets THC from CB1 receptors, thereby limiting its efficacy (pharmacodynamics). A different study found that in high CBD low THC formulations, CBD offsets the psychiatric effects of THC.
With this, the debate on whether and how to combine THC with CBD continues.