Nip it In the Bud: Cannabis Use and Intimate Partner Violence

By: Mitchell Colbert

 

 

The old trope of cannabis making users outrageously violent is as old as Harry Anslinger’s Gore File, yet despite evidence to the contrary, this myth has stuck around and taken new forms over the years.

A new study by UC Davis and Duke University is making headlines, purporting to show that cannabis use may increase the rate of intimate partner violence (IPV) and lead to overall worse life outcomes in middle age. 

Dr. Magdalena Cerdá and her colleagues at Duke University are the most recent group of researchers to use the Dunedin Multidisciplinary Health and Development Research Unit’s (DMHDRU) data on 1,037 babies born in Dunedin, New Zealand between 1972-73. 

The DMHDRU has been following those children all through their lives and now the study is in its fifth decade; along the way over 1,000 scholars have used this data for analysis, including Dr. Cerdá. 

This is important to note, because none of the researchers in this current study had any say in how the original data was collected, how accurate it may be, how questions were asked, etc. It is also worth noting that previous studies using the Dunedin sample to make claims about cannabis use have been debunked for failing to control for confounding variables, such as socioeconomic status and other drug/alcohol use.

In Rogeberg’s discussion of the Dunedin study, he makes the point that “extensive publications on the Dunedin cohort indicate that early-onset cannabis use is more common for those with poor self-control, prior conduct problems, and high scores on risk factors.” He adds that “based on results from a similar cohort, a likely consequence of this is that Māori participants will be overrepresented.”

The Māori are the indigenous Polynesian people of New Zealand, and, as of the 2013 census, the largest ethnic minority in the country at 15% of the population (followed by Asians [12%], Pacific Peoples [7%], and the catch-all “MELAA” Middle Eastern/Latin American/African [1%]).

While the Māori are the second largest racial group in New Zealand, in the US, the Māori population is so low the census does not keep records of them as a specific group; Wikipedia says there are under 4,000 Māori in all of America.

The entire population of New Zealand is 4.67 million people, roughly the same as Louisiana. Additionally, even though it is totally illegal in New Zealand, cannabis is used at an even higher rate than it is in the US.

Clearly, for many reasons, New Zealand is not America, and extrapolating from one country to another is not guaranteed any measure of accuracy. This issue is compounded when you have American researchers deciding how to control for another culture’s socio-cultural factors; put another way, how can someone who has never been raised in a given culture know how to control for culture-specific factors?

This is evident in Dr. Cerdá’s study, which doesn’t mention the Māori once in the entire publication, and perhaps did not adequately control for confounding variables related to their likely over-representation in the sample.

It is further worth noting that the entire Dunedin sample is 1,037 (Margin of Error = 3%), but only about 18% of the sample used cannabis, reducing the actual sample size in Cerdá’s study of cannabis users to be closer to 200 people (Closer to a 7% MoE), and making the results much less accurate and even harder to generalize than the Dunedin study itself.

Dr. Cerdá herself is realistic about her research, mentioning in the discussion section that, “the findings are particular to a cohort of individuals born in Dunedin, New Zealand, in the 1970s and may not generalize to groups exposed to different social norms regarding cannabis use or a different set of economic and social circumstances.”

Dr. Cerdá added that the “prevalence of cannabis dependence is higher among New Zealanders than in other developed nations.” She also cautioned that their “findings should be considered in light of limitations…the study took place in a setting in which cannabis is illegal—the question remains whether the same consequences would arise in a setting in which cannabis is legal.”

Finally, Dr. Cerdá made it clear that the researchers “do not purport to report a causal relationship between cannabis dependence and economic/social problems [but] cannabis dependence could be a marker of a life trajectory characterized by social and economic adversity.”

As Dr. Cerdá points out, a major reason for jail time, fines, and numerous other issues, which led directly to the downward trend they observed, was because the drug war makes criminals out of people who seek to use a plant which is safer than alcohol.

Bearing all of this in mind, when I heard that one of their findings was that “persistent cannabis dependence (and regular cannabis use) was also associated with … higher rates of intimate relationship conflict, including physical violence and controlling abuse,” I had serious doubts.

It seemed Dr. Cerdá and her colleagues missed a major study out of the University of Buffalo, which used more recent data about actual Americans to make conclusions about how cannabis effects IPV.

Actually in America:

Dr. Philip Smith and colleagues at the University of Buffalo released a study two years ago, using data from a decade-long longitudinal study from New York which was completed in 2006, and yielded data which is not only more culturally relevant to those living in America, but also thirty years more up to date than Dunedin. 

While previous “research on the association between marijuana use and IPV has generated inconsistent findings,” Dr. Smith found that, using fully adjusted models, “more frequent marijuana use by husbands and wives predicted less frequent IPV perpetration by husbands. Husbands’ marijuana use also predicted less frequent IPV perpetration by wives.” 

If you’re beginning to think that only husband’s use matters, “Moderation analyses demonstrated that couples in which both spouses used marijuana frequently reported the least frequent IPV perpetration.” 

The only group found to have any increase in rates of IPV were “wives who had already reported IPV perpetration during the year prior to marriage,” in other words, only women with a history of abuse were more likely to perpetrate more IPV because of increased use of cannabis.

Dr. Smith’s study, like Dunedin and nearly all studies on cannabis, did not record the amount or potency of cannabis consumed, just the frequency of usage. 

Without knowing the dosage of cannabis consumed, whether it was CBD or THC-rich, and other factors any findings will have little relevance as they cannot be replicated in other studies. 

Until more studies come out shedding light on this topic, ideally ones which record dosage information, the topic of whether cannabis leads to more intimate partner violence has been nipped in the bud, and for those of us in America it seems the answer is most likely no but it really kind of depends.