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.
Stream your PBS favorites with the PBS app: https://to.pbs.org/2Jb8twG
Find more from PBS NewsHour at https://www.pbs.org/newshour
