We all know not every strain of marijuana is the same. But are some forms of cannabis safer than others? According to a new study, the answer is yes.

Scientists have found that marijuana that contains the compound cannabidiol (CBD) has less long-term effects than marijuana without it. In an experiment, the researchers injected two groups of mice with doses of tetrahydrocannabinol (THC). One group received only the THC, while the other also received a dose of CBD. They found that the mice that received only THC experienced greater anxiety and memory impairment over the long term, while those dosed with CBD experienced none of those side effects.

Dr. Ken Mackie, a professor at Indiana University and one of the study's authors, says the experiment "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." They also noted that over the last several decades, the amount of THC in marijuana has increased about 300 percent while the amount of CBD has actually decreased. 

Previous studies on the effects of CBD on THC have been mixed. A 2013 study showed that subjects who smoked marijuana with high amounts of CBD were unlikely to experience anxiety as a result. And another from 2011 showed that people who smoked marijuana with CBD were less likely to exhibit psychotic symptoms. But neither of these studies were replicated by other scientists.

Mackie says his study is more reliable than those in the past because, "This is the first study in a rigorously controlled animal model to find that CBD appears to protect the brain against the negative effects of chronic THC."

Earlier this year, the Canadian government recommended that citizens use marijuana with high amounts of CBD and considered these products to be "low risk."

While further research is still needed to figure out how CBD counteracts the effects of THC, it may be a good idea to keep that information in your pocket next time you hit a dispensary.