Over the past 20 years, 23 states and the District of Columbia have legalized marijuana for medical use. Despite these changes to state laws, opponents continue to argue that marijuana causes more harm than good. A new study refutes their claims and shows that marijuana is safer than alcohol and tobacco, and researchers and policymakers may have overestimated the risks associated with its use.
Researchers Use Novel Approach to Compare Mortality Risks
Research conducted by Dirk Lachenmeier and Jürgen Rehm, and published in Scientific Reports in January 2015, investigated the mortality risk associated with seven substances by comparing the lethal dose of each substance with the typical amount used. This ratio, referred to as the margin of exposure (MOE), was used to determine the risk of dying from an overdose of each of the substances.
The MOE is a novel method for comparing the mortality risk of different substances. Introduced by the European Food Safety Authority in 2005 as an approach for assessing the risk of toxic compounds, it had only ever been used in the addiction field for evaluating substances in alcoholic beverages. Previous attempts to compare the dangers of substances of abuse were based largely on anecdotal, rather than scientific, evidence, which meant that policymakers had to rely on educated guesses and survey data from developed nations when making legislative decisions. Only in the past decade have researchers begun to use robust scientific techniques to classify the mortality risks of particular substances of abuse. However, many of these approaches were based on expert panel judgments on harm indicators, such as intoxication and physical and psychological dependence.
Evidence for Marijuana's Safety Grows
Lachenmeier and Rehm's research revealed that, of all the substances analyzed, alcohol posed the highest mortality risk at an individual level, followed by heroin, cocaine, tobacco, ecstasy, methamphetamine and marijuana. Alcohol was found to be about 114 times more deadly than marijuana, which was the only substance that was classified as having a low mortality risk. The researchers' classifications were based solely on the substances themselves and did not take into account environmental risk factors, such as the sharing of contaminated needles by intravenous drug users. Previous studies, including a comparison of the toxicity of commonly abused substances published in the journal Addiction in June 2004, ranked marijuana as safer than alcohol and tobacco, but it was not known that the discrepancy between their mortality risks was this large.
Researchers Call for Changes to Federal Marijuana Laws
Despite their known health risks, alcohol and tobacco are exempted from the Controlled Substances Act due to cultural and economic reasons. Alcohol and tobacco have been acceptable substances in U.S. culture since well before the repeal of Prohibition in 1933, and they are two of the most widely used substances nationally. The researchers believe that the risks of alcohol and tobacco may have been underestimated in the past, and are urging federal government to focus their efforts more on mitigating the harmful effects of alcohol and tobacco than on other substances, such as marijuana.
In contrast, the risks of marijuana may have been overestimated. For the mortality endpoint alone, the findings showed marijuana's MOE to be above safety thresholds at the individual and population levels. There has never been a case of a cannabis overdose death. This lends weight to the argument that marijuana should be removed from Schedule I of the Controlled Substances Act, a category reserved for the most dangerous substances.