Web MD – The active chemical in marijuana promotes the death of brain cancer cells by essentially helping them feed upon themselves, researchers in Spain report. Guillermo Velasco and colleagues at Complutense University in Spain have found that the active ingredient in marijuana, THC, causes brain cancer cells to undergo a process called autophagy. Autophagy is the breakdown of a cell that occurs when the cell essentially self-digests. . . The findings appear in the April 1 issue of the Journal of Clinical Investigation.