Where is this fact coming from?
This fact comes from the countless amount of assessments I've done on pot smokers over the last 1.5 years that met the required criteria for substance dependence as per the DSM-IV pg 181.
Criteria for Substance Dependence
A maladaptive pattern of substance use, leading to clinically significant impairment or distress, as manifested by three (or more) of the following.
1. Tolerance, as defined by either of the following:
(a) a need for markedly increased amounts of the substance to achieve intoxication or desired effect.
(b) markedly diminished effect with continued use of the same amount of the substance
2. withdrawal,, as manifested by either of the following:
(a) the characteristic withdrawl syndrome for the substance (refer to Criteria A and B of the criteria sets for Withdrawal from the specific substances.)
(b) the same (or a closely related) substance is taken to relieve or avoid withdrawal symptoms
3. the substance is often taken in larger amounts or over a longer period than was intended
4. there is a persistent desire or unsuccessful efforts to cut down or control substance use
5. a great deal of time is spent in activities necessary to obtain the substance (eg visiting multiple doctors or driving long distances), use the substance (eg chain-smoking), or recover from its effects
6. important social, occupational, or recreational activities are given up or reduced because of substance use
7. the substance use is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance (eg current cocaine use despite recognition of cocaine-induced depression, or continued drinking despite recognition that an ulcer was made worse by alcohol consumption)
There is also some evidence to support physiological dependence to it as well. Many of our clients that quit smoking reported having withdrawal symptoms when they quit smoking it. To name a few: irritability, increased anxiety, change in sleep pattern, depression. I'm not saying it is physiologically dependent but there is a positive correlation there worth researching a bit more.