"There are two strains of marijuana called sativa and indica. The sativa increases dopamine and gives you energy while decreasing pain threshold. Indica is a "sleepy high," she explained."
Also..
http://en.wikipedia.org/wiki/Analgesic
"Tetrahydrocannabinol (THC) and some other cannabinoids, either from the Cannabis sativa plant or synthetic, have analgesic properties, although the use of cannabis derivatives is currently illegal in many countries."
Personally I'd like to think that maybe he had a mental condition and the weed only made the situation worse.