Rates of teen marijuana use in Canada are among the highest in the world. Legalization advocates blame high use on criminalization: "the ready availability from dealers with no scruples about targeting youth, and the cachet of forbidden fruit—or rather, buds." Indeed, the first objective of the Canadian federal government's marijuana legalization agenda is to "Protect young Canadians by keeping marijuana out of the hands of children and youth.
Yet can legalization actually reduce youth marijuana use?
A basic supply and demand analysis can help clarify the issues. The diagram below shows stylized marijuana supply and demand curves. Because the market is competitive, the supply price is cost-driven: it reflects the marginal costs of producing and distributing marijuana, including the expected costs of any criminal penalties associated with drug trafficking.
The legalization-reduces-youth-drug-use argument goes like this: taxing cannabis, plus imposing strict penalties on those who distribute drugs to youth, will increase the price of marijuana. Public health campaigns emphasizing the risks of marijuana use will dampen the demand. The net impact will be to reduce marijuana use:
Unfortunately, this pleasing scenario is unlikely to come to pass. It will be difficult to impose high taxes on recreational marijuana use. Because medical marijuana is untaxed, if the taxes on recreational use are too high, people will find an excuse to switch to medicinal products. This is not merely a hypothetical possibility: in Colorado, medical marijuana sales volumes are larger now than they were immediately post-legalization (based on data found here).
Second, marijuana is not that difficult to grow (though it's not that easy, either - see the threads in this 420 forum). If marijuana taxes are too high, people will evade the taxes by switching to home grown. The level of taxation that the recreational marijuana market will bear is unknown, but my betting is that the after-tax price of legal marijuana will be closer to the price of beer than to the price of single malt whiskey.
What about the argument that legalization will drive unprincipled drug traffickers out of business and, with only legitimate enterprises selling pot, it will be easier to control sales to minors? One piece of evidence on the effect of age restrictions on consumption comes from the alcohol market, and is summarized by Kitt Carpenter and Carlos Dobkin in this ungated paper (see p. 147 onwards). Their estimates suggest that age prohibitions are associated with roughly a 10 to 20 percent reduction in use. So, for example, 20 year olds, who can't legally purchase alcohol in the US, drink roughly 10 to 20 percent less than those just over the legal drinking age.
So, yes, age restrictions do dampen use, but the impacts are not large. Public health campaigns might also discourage use. Set against this, however, is that legalization of recreational marijuana, together with capital investment, is leading to innovation, new product development, and branding. Take, for example, a high-end boutique product such as Mr Moxey's CDB Ginger Mints. It's an edible, there's no more of that potentially embarrassing trying-to-inhale-without-coughing business. Indeed, the ginger and mint in Mr Moxey's leaves your breath smelling fresh. It's a branded, which means (one hopes), that it is a known quantity; a reliable product. There's no need to worry about getting bad quality or adulterated weed. Moreover innovative growing and processing practices are allowing producers to isolate particular cannabinoids. For example, Mr Moxey's mints have high concentrations of CDB (the "body high" with analgesic, anti-inflammatory, and anti-anxiety properties), and relatively less THC (the more psychoactive cannabinoid that produces a "stoned" feeling). The availability of high quality, reliable products would be expected to shift demand outwards, counteracting the effect of public health campaigns and age restrictions.
One additional complicating factor is that, if marijuana was legalized, and capital investment was able to flow into the industry, scale economies could lead to significant reductions in production costs, shifting the supply of marijuana to the right. Another complication is that, if marijuana use was legalized, shifting social norms could lead to an upwards trend in use. Marijuana wouldn't just be for the stoner kids hanging out in the smoke pit anymore - and as it became more mainstream, more people might be tempted to use it.
In sum, it is hard to predict the impact of marijuana legalization on youth consumption. But if I had to guess, I would expect the net effect of all of the factors above to be something like this:
Any reductions in consumption by current users would be offset by the entry of new users attracted by better quality, more reliable, safer products. However there is simply not enough empirical evidence to know for sure what the impact of legalization on youth consumption will be. This paper finds that legalization of medical marijuana increases adolescent drug use, this paper finds that easier marijuana access is associated with use at a younger age, but this paper found that teenage use decreased when medical marijuana was legalized.
Even if decriminalization is associated with increased use, does this mean that marijuana legalization is a bad thing? No. Consumption is not the same thing as harm. It is possible for youth marijuana consumption to go up and the harms associated with youth marijuana use to go down if youth are using products more moderately, and are using better quality products. Moreover, even if marijuana is harmful, policies to restrict marijuana use are also harmful - like imprisoning people. But these are complex issues, and beyond the scope of this post. The point here is simply to unpack the claim that legalization will decrease marijuana use among teens.