CBD Did Not Offset THC’s Acute Effects in a Randomized Human Trial
A randomized human trial found no evidence that cannabidiol (CBD) reduced the short-term cognitive, psychological or physiological effects of tetrahydrocannabinol (THC) when the two compounds were inhaled together.
The study, published online in 2022 in Neuropsychopharmacology, tested whether increasing the CBD content of cannabis could make its effects safer. Its authors found that CBD did not protect against THC-related memory impairment or increases in psychotic-like symptoms at the CBD-to-THC ratios examined. Read the original randomized trial.
What the researchers tested
The double-blind, crossover trial included 46 healthy adults who used cannabis infrequently. Participants inhaled vaporized cannabis containing a fixed 10-milligram dose of THC, combined with either no CBD or 10, 20 or 30 milligrams of CBD. Each participant received all four preparations in a randomized order, allowing the researchers to compare the different ratios within the same people.
The primary measure was delayed verbal recall, assessed with the Hopkins Verbal Learning Task. Researchers also evaluated immediate memory, working memory, psychotic symptoms using the positive subscale of the Positive and Negative Syndrome Scale, subjective enjoyment of music and chocolate, heart rate, blood pressure, body temperature and persecutory thoughts.
CBD did not blunt the main effects of THC
THC impaired delayed verbal recall and increased positive psychotic symptoms compared with baseline. Adding CBD did not significantly change either effect, even as participants’ blood CBD concentrations rose with the dose.
The study also found no meaningful CBD-related reduction in other cognitive, subjective or physiological effects of THC. Participants reported similar levels of euphoria across the preparations, while heart rate increased after inhalation. Coughing was more common at the higher CBD-to-THC ratios, possibly because participants needed to inhale for longer to receive the intended dose.
These results do not show that CBD can never influence THC’s effects. They apply specifically to a single inhaled dose, the tested amounts and ratios, and a group of healthy, infrequent cannabis users. The findings may not predict what happens with oral CBD, different THC doses, regular cannabis use, long-term exposure or other combinations of cannabinoids.
What the findings mean
Claims that CBD automatically counteracts THC’s unwanted effects are not supported by this trial. The researchers noted that products described as “high CBD” may appear less intoxicating primarily because they contain less THC, rather than because CBD neutralizes THC’s effects.
More research is needed to determine whether the timing, route of administration or dose of CBD changes its interaction with THC. Earlier laboratory studies have reported differing results, so the effect may depend on how the compounds are administered and on the characteristics of the people using them.
Consumers should also distinguish between evidence for a specific prescription CBD medicine and claims made about commercially sold CBD products. The U.S. Food and Drug Administration’s CBD guidance notes that many marketed products have not been evaluated for safety, effectiveness, dosage or drug interactions.
