Daniele Piomelli, the Louise Turner Arnold Chair in the Neurosciences, will appear on “Drugged: High on Marijuana,” which airs at 8 p.m. Sunday, Jan. 16, on the National Geographic Channel. The show will explore in detail how the most widely used illicit drug on the planet works inside the body. Piomelli will discuss the effects of cannabis on the brain and its potential medicinal purposes. His own groundbreaking research is showing how the body’s endocannabinoid system can be targeted by new treatments to combat anxiety, depression and obesity.