A number of studies suggest that alcohol and cannabis (marijuana) are economic substitutes, meaning that when one increases, the other tends to (albeit unequally) decrease. The past five years are one example of such opposing trends. Thus, one apparent unintended consequence of raising the drinking age to 21 was a modest increase in cannabis use among 18-20 year olds and high school seniors.
The most recent study by Crost and Guerrero (2011) found that, using a regression discontinuity approach, upon turning 21 young adults tend to increase their drinking and decrease their cannabis use, both in terms of probability and frequency. The authors estimate from this pattern that the 21 drinking age law decreases past-month alcohol use by 16% while increasing past-month cannabis use by 10% among 18-20 year olds. The apparently larger effect size for alcohol may reflect greater reporting bias of drinking (which is illegal before 21 but legal afterward) relative to cannabis use (which is illegal for all ages), so the real effect on alcohol may be considerably smaller. This study dovetails nicely with an older study by DiNardo and Lemieux (2001), which found that raising the drinking age to 21 in the 1980s led to a decrease in self-reported alcohol use accompanied by an increase in self-reported cannabis use by high school seniors, though both effects were fairly small. It also dovetails somewhat with the webmaster's own (albeit unscientific) observations of his peers' behavior in high school and especially college.
Further evidence for substitution effects can be found in another recent study by Anderson and Rees (2011). This study found that legalization of medical cannabis was associated with a modest increase in self-reported cannabis use among young adults aged 18-25 (but not among people under 18) and a modest decrease in alcohol sales and consumption. Even more notably, legalization of medical cannabis was associated with a 9% decrease in traffic fatailites, which was most likely a result of reduced alcohol consumption. Also, the same DiNardo and Lemieux study mentioned before found that state-level decriminalization of cannabis was associated with a decrease in drinking among high school seniors, even though there was no corresponding increase in cannabis use (actually, both went down). Interestingly, in contrast to the effects of the drinking age, higher beer taxes were found to reduce both alcohol and cannabis use.
So is this apparent substitution effect of the 21 drinking age a good thing or a bad thing? While it is true that unadulterated cannabis is generally safer than alcohol by just about any objective measure of harmfulness, neither substance is absolutely safe for everyone, and most of the pro-21 crowd would probably not be very thrilled about an increase in cannabis use. Furthermore, reporting bias may very well overstate the effects of the drinking age on alcohol (but not cannabis) use, and thus the net effect is uncertain. Even though probability and frequency of drinking may be reduced somewhat by a 21 drinking age, the intensity of the clandestine drinking that remains may very well increase to more dangerous levels for a variety of reasons. More ominously, though there have been no direct studies to our knowledge of the effects of the drinking age on hardcore drug (cocaine, heroin, methamphetamine, etc.) or prescription drug abuse among teens and young adults, it is nonetheless plausible that there may be some substitution of those more dangerous substances for alcohol as well. After all, the crack epidemic of the late 1980s and early 1990s roughly coincided with the drinking age being raised to 21, and the more recent increase in prescription drug abuse coincided with increasingly tougher enforcement of the 21 drinking age. And while the gateway drug theory is largely a bogus concept, as long as cannabis remains illegal, users will continue to expose themselves to dealers who may also be peddling more dangerous wares.
While Twenty-One Debunked does not take an explicit position on whether cannabis should be legalized, it should be noted that our parent organization, the True Spirit of America Party (TSAP), fully supports cannabis legalization for all adults 18 and over. And Twenty-One Debunked believes that, if and when cannabis does become legal, the age limit should be 18 rather than 21, for many of the same reasons that we believe that the drinking age should be lowered to 18.
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