According to a new study in mice, marijuana with high levels of cannabidiol may be less risky to smoke over the long term, because this ingredient could counteract the plant's more harmful effects.
Adolescent mice that were injected with frequent doses of tetrahydrocannabinol (THC) showed signs of memory loss and increased anxiety over time. But mice that received doses of THC with equal amounts cannabidiol (CBD) didn’t experience these negative effects.
The study "suggests that strains of cannabis with similar levels of CBD and THC would pose significantly less long-term risk due to CBD's protective effect against THC," sad the author of the study.
Another study, published in 2011, found that people who tended to use marijuana products with high CBD levels were at lower risk for psychotic symptoms over the long term.
In this new study, the researchers examined the effects of THC and CBD on both adolescent and adult mice. The mice were divided into five groups: a group that received THC only; a group that received CBD only; a group that received THC and CBD; a group that received a placebo; and a group that received no treatment. The mice in the first four groups were injected with the substances every day for three weeks. The researchers examined the mice shortly after their drug treatment and after a six-week drug-free period.
The researchers found that, immediately after treatment, the mice exposed to THC alone showed signs of impaired memory and increased obsessive-compulsive behavior. Six weeks later, the adolescent mice still showed these symptoms, while the adult mice did not. (This finding agrees with research in humans suggesting that teens may be at greater risk for long-term problems from marijuana, compared with adults.) However, mice that were exposed to both THC and CBD together showed no changes in their behavior at all.
More studies are also needed to determine how CBD counters the effects of THC, and how much CBD is needed to confer a protective effect, the researchers said.