How Heavy Marijuana Use May Hurt the Developing Brain: An Animal Study

With legalization of recreational marijuana use accomplished in two states and likely in many more, concerns about how it may affect youth are becoming more prominent than ever. To examine cognitive issues, investigators intravenously administered vehicle or Δ⁹-tetrahydrocannabinol (THC) at a dose equivalent to one or two marijuana cigarettes 5 days per week for 6 months to seven matched pairs of male adolescent rhesus monkeys.

The monkeys were repeatedly assessed for spatial memory (i.e., recalling the quadrant of a computer touch screen in which a square appeared) and object memory (i.e., recalling the color and shape of an object presented on the screen). With THC, improvement in accuracy (expected because of age and practice effects) was…