No need to get your panties in a wad, just smoke some more "American", apparently it's your favorite./sarc
As to my point, there are several studies out there, but please use some common sense. Like any other agricultural "product" marijuana has been modified and selectively bred over a period of decades for increased profit and potency.
http://collections.ic.gc.ca/drug/articles/marijuana/m_hi_tpr.htm
Are you from Canada? Since the link is I thought you might be as well.