I wanted to add to your story a little bit. The US government started to refer to cannabis (or hemp as it was also known) as marijuana prior to it's prohibition. The US citizens didn't know what marijuana was; all they knew was that it caused something called "reefer madness". So when the government wanted to make marijuana illegal, the public went for it. Only after that happened, did the people find out what was really going on.

Anyways, I use the word cannabis when I am talking about it in a more formal, or medical sense. Informally I use bud, weed, or marijuana. I also like saying the word reefer. lol.