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PBS News Hour

Scientists race to learn how marijuana affects the brain

Season 2019 Episode 215 | 9m 22s

As national attitudes and laws around cannabis use have evolved, so have the commercially grown strains of the plant. Some marijuana varieties today contain levels of THC, the drug’s psychoactive compound, as high as 50 percent, compared to around 5 percent a generation ago. But as science correspondent Miles O'Brien reports, the effects of cannabis on the human brain are still relatively unknown.

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