BBC has some good information on Marijuana...
http://news.bbc.co.uk/1/hi/help/3681938.stmOr if that doesn't work...
http://news.bbc.co.uk/1/hi/programmes/panorama/4082196.stm and click on Watch The Programme
Nice 40 minute video, but worth it if you got the time

Personally I have enough health problems, adding more isn't my plan