Does Strong Marijuana Cause Addiction?

Strong pot matters, but maybe not the way we think.

Colorado, Washington, and some 20 additional states have now made various provisions for legal transactions involving marijuana. And since time immemorial, there has been an illegal market for marijuana. But try getting your hands on some marijuana straightforwardly, through appropriate channels, for purposes of medical research, and, well, most researchers have just said forget it.

Because in the U.S., a bizarre system of drug classification has led to the ludicrous situation of a virtual government monopoly on cannabis for experimental purposes. Can’t researchers just walk around this roadblock and procure pot in some manner that is legal in their state? No, they cannot—not if they want any serious research grants, or publication in refereed journals. Without the federal government imprimatur, marijuana research isn’t kosher, and could put researchers at legal risk. Researchers who go through channels report frequent and unpredictable delays, and this has been true for decades. Yet millions of recreational marijuana users can secure a supply of the drug, often accompanied by specific genetic information, often with relatively little effort.

The Drug Enforcement Administration (DEA) has refused to budge on its opposition to petitions for reclassification of cannabis. A recent Washington Post article  attributed the problem to “stigma associated with the drug, lack of funding and legal issues…. Scientists say they are frustrated that the federal government has not made any efforts to speed the process of research.”

However, as almost everyone knows, things are different in The Netherlands. It isn’t a big problem for researchers at the University of Amsterdam and elsewhere in that country to engage in behavioral studies of actual marijuana smokers. Participants in a recent study, the results of which appear in Addiction, were even allowed to use their own weed. (Thanks to Ivan Oransky for bringing this study to my attention.) The thesis being tested by Peggy van der Pol and colleagues is a familiar one: Do marijuana smokers “titrate” very strong pot—that is, do they modify their smoking/dosing behavior accordingly, in order to reduce overall THC exposure? If so, just because a cannabis user is ingesting high-THC plant material doesn’t mean that his or her THC blood levels are that much higher than smokers of less potent weed. But if this is NOT true—if smokers of strong pot are boosting their THC exposure significantly, the results could conceivably include impaired driving and greater rates of marijuana addiction.

Most studies that attempt to estimate the risk of cannabis dependence in pot smokers rely on a familiar yardstick—the number of days a smoker smokes per month. Dosing behavior, and other behavioral aspects of marijuana smoking that affect THC exposure, are usually ignored. The Dutch researchers found that, in a group of 600 frequent cannabis users, some smokers did in fact show “shorter puff duration and inhaled lower smoke volumes when joints with a higher THC concentration were used.” So, yes, users did engage in partial titration when they smoked stronger marijuana. However, this did not translate into the expected results. In a final sample of 98 participants, the scientists discovered that “users of stronger cannabis generally used larger amounts of cannabis to prepare their regular joint.” (The study participants smoked marijuana European-style, mixing their marijuana with tobacco.) And even though subjects smoking joints with higher THC levels did inhale at slightly lower volumes and at a slower pace, the average user of pot with THC levels of 12% or higher definitely inhaled more liters of smoked THC per month than users of less potent pot. But just to confound matters, total THC exposure over a month’s time turned out to be “a weak predictor of dependence severity, and did not remain significant after adjustment for baseline dependence severity.”

Nonetheless, even with some degree of titration, “a positive association between total puff volume and withdrawal/craving was found, indicating that a larger inhaled volume may increase the THC exposure sufficiently to result in significant effects on clinical outcomes.” (Here is the UK National Health Service take on the research.) 

It is always difficult to say for certain in a prospective, cross-sectional study of behavior whether participants are acting the way they would act in “real life,” although efforts were made to allow smoking at home, or in Dutch coffee shops, as well as the laboratory. Interestingly, the one behavior that seemed to predict dependence in post-hoc analyses was a simple one. Smokers were allowed to mix a joint however they wished, and smoke however much of it they wanted to. Smokers who finished their joints, rather than leaving a portion of it for later, were the smokers more likely to be associated with dependence in the follow-up studies. In fact, “percentage of the joint smoked may be a simple proxy for risky smoking behavior.”

In addition, certain withdrawal symptoms correlated with dependence: “Increased somatic withdrawal symptoms are predictive of relapse, and…. increased physical tension is a significant predictor of relapse.”

As with alcohol, it seems that it is not necessarily how much you smoke or drink. It is how you smoke or drink. Strong marijuana doesn't cause addiction. The way certain people use strong pot can result in addiction, however.

Earlier research has shown that higher levels of cannabis dependence are associated with greater functional impairment, and that "the average level of impairment caused by cannabis, while mild for most users, can rise to the level of tobacco withdrawal which is of well established clinical significance.”

 Physical distress, a “somatic” variable, often matters more, in terms of relapse, than the amount of marijuana smoked, or any other symptom on the roster of functional impairments—including mood and other negative affect variables.  In an earlier study published in PLOS ONE,  investigators found that “cannabis withdrawal is clinically significant because it is associated with elevated functional impairment to normal daily activities, and the more severe the withdrawal is, the more severe the functional impairment is. Elevated functional impairment from a cluster of cannabis withdrawal symptoms is associated with relapse in more severely dependent users.”

van der Pol P., Liebregts N., Brunt T., van Amsterdam J., de Graaf R., Korf D.J., van den Brink W. & van Laar M. (2014). Cross-sectional and prospective relation of cannabis potency, dosing and smoking behaviour with cannabis dependence: an ecological study, Addiction,   n/a-n/a. DOI: 10.1111/add.12508