Reefer Madness Revisited

Chronic pain is a major problem in this country. To combat it, doctors are prescribing—some would say overprescribing—opioids such as Vicodin and OxyContin. Americans consume about 90% of the world's supply of these dangerous drugs. According to the Centers for Disease Control, opioid overdose deaths have increased from 4,030 in 1999 to 16, 651 in 2010. That's an average of 46 deaths per day, more than heroin and cocaine combined. Sixty percent of these folks have a legitimate doctor's prescription. If only someone could come up with a safer way of treating pain. . . . .

Marijuana has been shown to be effective in treating chronic pain. A survey of medical marijuana users in Canada found that 68% of them used it as a substitute for prescription drugs. The three main reasons given were fewer withdrawal symptoms, fewer side effects, and better symptom management. Marijuana can also be effectively combined with opioids to allow patients to use lower doses of opioids. If you can locate someone who has died from a marijuana overdose, you have a scoop. In July, New York became the twenty-third state to legalize marijuana for medical use.

Marcus Bachhuber and his colleagues published a new study of the effects of marijuana legalization on opiate deaths in the Journal of the American Medical Association this week. It's not a controlled experiment; it's a before-after comparison group design. While there is some ambiguity about how to interpret it, the study has a number of important strengths.

The authors counted opioid deaths on death certificates from all 50 states between 1999 and 2010. By 1999, three states (California, Oregon and Washington) had already legalized medical marijuana. Another ten states legalized it while the study was in progress. (The remaining ten states changed their laws after 2010.) The death rates from opioids were compared between those states that had legalized medical marijuana (the marijuana states) and those that had not (the comparison states). They also compared death rates within the marijuana states from before to after legalization. The design statistically controlled two variables that are known to affect the opioid death rate, the unemployment rate and state policies regulating prescription drugs.

• Those states in which medical marijuana was legal at the time had a 24.8% lower mean annual opioid mortality rate than the comparison states. The marijuana states had 1729 fewer death than would otherwise be expected in 2010 alone. The results were unchanged when suspected suicides were eliminated.
• In the ten states that legalized marijuana between 1999 and 2010, the drop in the death rate from opioids coincided with the change in the law. It took a couple of years for the full effect of the legal change to be realized. On average, the death rate dropped 20% in the first year, 25% in the second, and peaked at 33% in the fifth and sixth years.
  
  

In searching for possible hidden confounds, our attention is naturally draw toward possible differences between the marijuana and comparison states that might have affected overdose deaths. There is a possible selection bias. The marijuana states are more progressive, and it's possible, but not obvious, that political liberalism might reduce painkiller deaths in other ways. However, when the death rates are compared from before to after the legalization, the marijuana states become their own controls.

It is important to note that in order to explain the results, a potential confound would not only have to be more prevalent in the marijuana states, it would also have to have occurred at about the time legalization took effect. One of the strengths of this study is that the drop in deaths coincides with the onset of legalization even though the law changed at different times in different states. This makes it less plausible that historical events affecting several states simultaneously could account for the results.

Almost all news reports about this study quote drug experts who urge caution when drawing conclusions from the study, although they usually don't specify what they think is wrong with it. One expert, Dr. Andrew Kolodny, is quoted in Newsweek as suggesting that states that legalized medical marijuana might also impose more restrictions on the prescribing of painkillers, apparently not realizing that the authors had anticipated this possibility and found that prescription monitoring laws were not associated with lower overdose death rates. (The reporter did not correct his error, allowing readers to assume that he had made a valid point.) Of course, most articles also contain the obligatory vague words of warning about the alleged dangers of the devil's weed.

The study makes a fairly strong case for the immediate legalization of medical marijuana at the federal level and in the remaining states. Why is medical marijuana still illegal? As the Bachhuber study suggests, medical marijuana is a serious threat to the profits of pharmaceutical companies. Given the opportunity, chronic pain sufferers are likely to substitute marijuana for more expensive and dangerous prescription drugs. Journalist Lee Fang points out that the groups leading the fight against relaxing marijuana laws, such as the Partnership for Drug-Free Kids, receive a large portion of their funding from the pharmaceutical companies that market analgesic opioides. Several leading anti-marijuana academic experts also serve as paid consultants to big pharma. Here is Fang being interviewed by Chris Hayes.

As usual, we can say (this time, with enthusiasm) that more research is needed. The good news is that the Drug Enforcement Administration has increased its annual allotment of cannabis for clinical research from 21 kilograms to 650 kilograms—still too little—in response to demand from investigators.

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