JUDY WOODRUFF:

With recreational marijuana now legal in eight states, a serious health and safety question about the potency of the psychoactive drug in cannabis, known as THC, are emerging. In Colorado, some marijuana products contain 90 percent pure THC, with little research documenting the physical and mental effects on consumers.

This week, the state's health department announced more than $2 million in grants to study the impacts on driving and cognitive functioning.

As John Ferrugia of Rocky Mountain PBS in Denver reports, there are concerns that the effects on some users could be deadly.