How much cannabis does it take to kill a person?

Quite a lot. In fact so much that it's not possible according to the Canadian Senate Special Committee on Illegal Drugs.

"Cannabis presents almost no toxicity and cannot lead to an overdose." Summary Report regarding Toxicity of Cannabis.

"I've heard that you have to smoke something like 15,000 joints in 20 minutes to get a toxic amount of Delta9 THC. I challenge anybody to do that..."

Dr. Paul Horby, PhD Biochemist & Human Pathologist

"There are no deaths from cannabis use anywhere; you can't find one "

Dr. Lester Grinspoon, MD Professor Emeritus, Harvard Medical School