Marijuana is the most widely used illicit substance in the United States. On the ballot in California in the upcoming election is Proposition 19, an initiative to legalize marijuana. The state-initiated proposal, the Regulate, Control and Tax Cannabis Act of 2010, would legalize personal possession of up to one ounce, and regulate and tax the growing and sale of cannabis. One of the key goals of the initiative is taxation, with large amounts of revenue expected to flow into California’s empty coffers. The ability to tax and regulate what is currently an illegal drug has long been a chief argument advanced in favor of legalizing marijuana. An assortment of strange bedfellows have rallied on both sides of the debate in California: some stoners oppose the law as too restrictive, while anti-drug groups oppose it for not being restrictive enough. Republican and Democratic politicians, district attorneys, and police chiefs support it, citing, among other things, the savings to law enforcement, the legal system, and the penal system associated with decriminalizing marijuana use and possession. Current polls show the voters of California are about evenly divided on the matter.
An additional claim frequently offered in support of legalization is that marijuana is no more dangerous than tobacco and alcohol, both of which are legal. Is that claim true? The short-term effects of marijuana use — memory impairment, stimulation of appetite, disruption of psychomotor behavior, etc. — are well-known, and of course, comical, if the career of Cheech & Chong is any indication. Needless to say, there are reasonable concerns about public safety should decriminalization result in larger numbers of marijuana users driving or working while impaired. There is conflicting evidence on the long-term effects of cannabis use. In animal studies, long-term cannabinoid administration has been shown to be neurotoxic, resulting in decreases in neuronal volume, and neuronal and synaptic density. Less is known about the effects of long-term exposure in humans, and only a handful of brain imaging studies have been conducted, with inconsistent findings. An Australian MRI study, for example, revealed reduced hippocampal and amygdala volumes in long-term, heavy users with no history of polydrug use. Users performed significantly worse than controls on verbal learning (Yucel et al, Arch Gen Psychiatry. 2008;65(6):694-701). Matochik et al employed voxel-based morphometry and found differences in grey and white matter tissue density between heavy marijuana users and non-users (Matochik et al Drug and Alcohol Dependence 2005;77:23-30). Still other studies have shown both neurotoxic and neuroprotective effects of cannabis use.
The evidence for the safety (or danger) of recreational marijuana use, thus far, is inconclusive, and supports neither legalizing nor criminalizing cannabis. The matter warrants further study, particularly if decriminalizing becomes a more widespread phenomenon. As cash-strapped states look for creative solutions to their fiscal problems, it could be that legalizing marijuana will increasingly be viewed not as a public scourge but as a potential revenue stream — like the taxation of alcohol and tobacco. Should that happen, concern will shift to practical control of the predictable social and public health consequences of legal marijuana use.
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