You need to provide references for the "Marijuana often has physical withdrawal symptoms for chronic users" statement, because I pay attention to this type of stuff and I've never heard or or run across it in real life. Of course, opium addiction and withdrawal are well documented.
I'm not the same poster as above but a bit of Googling turned up several sources that appear reputable though I didn't dig real deep. I have no dog in this fight whatsoever but here's a link to one that I found interesting & that seems to have been well-conducted at first glance:
