This report?

Junky monkeys - 16 October 2000 - New Scientist

Scientists showed monkeys a lever to push to inject themselves with marijuana, and some of them did it 30x in an hour. It shows that monkeys "strive to inject themselves with the active chemical in marijuana in the same way that they seek out cocaine or morphine."

I'm not sure what to think, and I'm not sure I care. I started smoking bud 2 years ago, and I've breaked for 4 months, smoked for 3, breaked for 3 months, smoked for four, breaked for 7 months, smoked for two, and break for another month. I have no problem with it, so I won't worry about it. I'm waiting to see what other reports come out over the physical addiction though.