• Adverse health effects;
  • cannabis use;
  • design choice;
  • illegal supply;
  • legalization;
  • price effects.

Although some countries have quasi-legalized cannabis use (the Netherlands), made cannabis available for medical purposes (California currently has more than 1000 medical marijuana shops) or allowed the growing of a small number of cannabis plants for personal use (Australia), in most countries (the Netherlands included) cannabis supply, distribution and use is prohibited [1]. Nevertheless, cannabis is the most popular illicit drug. In 2009, between 2.8% and 4.5% of the world population aged 15–64 years, corresponding to between 125 and 203 million people, had used cannabis at least once in the past year [2]. Clearly, prohibition does not work and the debate on legalization of cannabis gains momentum. This debate is often emotional, with strong views of both proponents and opponents. Those who are in favour of legalization tend to ignore the negative health effects of cannabis use. Those who are against legalization ignore the fact that legal substances such as alcohol and tobacco also have bad health effects [3].

Caulkins et al. [4] provide an interesting contribution to the legalization debate. Rather than discussing the pros and cons of legalization they discuss legalization design choices: the level of taxes and whether taxes should depend on cannabinoid levels, rules on home cultivation, advertising restrictions and design adjustments over time.

The use of cannabis is widespread, but many individuals use for only a short period. Others use it on a regular basis, but are still recreational users for whom cannabis use is comparable to drinking a beer every now and then. It is difficult to predict what will happen if such an unprecedented policy change as legalization of cannabis is introduced. Legalization will affect cannabis use mainly—although not exclusively—through the change in price, which in itself will depend upon one of the legalization design choices, the level of taxes. When considering price effects, the dynamics of cannabis use are important. Usually, some youngsters start using cannabis between ages 15 and 25 years. If they have not done so before age 25 they are very unlikely to do this later in life. From an Amsterdam study it appears that about half of youngsters start using cannabis, but about 20% of them use cannabis for less than 1 year. Median duration of use is about 10 years, while about 30% of users persist [5].

There is hardly any study on the relationship between cannabis price and dynamics in use. A study based on Australian data shows that a lower price lowers the age of initiation but has no effect on the duration of cannabis use [6]. It is also not immediately clear how the intensity of cannabis use will change. It could be that a price drop affects only the extensive margin, i.e. attracts casual users without increasing frequent use. It could also be that a price reduction does not affect overall use but does affect frequent use. The effects of a cannabis price drop are likely to be strongest for youngsters. For the purpose of illustration, Fig. 1 shows the association between cannabis price and cannabis use of American youngsters.


Figure 1. The association between cannabis prices and cannabis use of youngsters; United States 1991–2007. (a) Ever cannabis use (%); (b) cannabis use last 30 days (%). Source: Cannabis use among 9th to 12th graders: Youth Risk Behavior Survey; median cannabis price in constant 2007 dollars per gram for small quantities (less than 10 g) [14]

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In the period 1991–1997 in the United States there was a drop in real cannabis prices of almost 60%, while between 1997 and 2007 cannabis price increased by 150%. These price fluctuations were accompanied by changes in ever use between 30 and 45% and changes in last 30 days use between 15 and 25%. Although the plots in Fig. 1 cannot be interpreted as causal, they suggest that both intensive and extensive margins of cannabis use will be affected by legalization. Legalization might cause a drop in cannabis price of 75% [7]. Although this is substantial, it is within the range of actual price changes in the United States in past decades. The price drop caused by legalization would mean no more than a return to mid-1990s prices.

There is a large epidemiological literature on adverse health effects [8] and recent evidence suggests that there is a negative causal effect of cannabis use on health [9,10], but in the grand scheme of risky health behaviours cannabis use has a modest contribution [11]. All the linkages to assess the health effects of legalization have one element in common: uncertainty. Therefore, opinions of individuals who have had personal experience with cannabis use may be helpful. From an analysis of Australian data it appears that past cannabis users are more in favour of legalization than non-users. Apparently, for individuals with personal experience the pros of legalization are more important than the cons [12].

The legalization design choices Caulkins et al. [4] discuss are important. It seems to me that taxes should be sufficiently high to discourage cannabis use and sufficiently low to drive out illegal supply. Furthermore, taxes should depend on cannabinoid levels, home cultivation should be allowed under restrictions and advertising should be banned. The nature of the legalization debate can be summarized in one word: ignorance. Therefore, the most important design choice of legalization is the flexibility to adjustment, allowing for learning by doing. There are many relationships about which researchers are uncertain, debating whether they are causal or mere associations. As long as nowhere in the world is cannabis legalized it is difficult to gain any clear idea about the consequences of legalization [13]. Removing the veil of ignorance that surrounds the legalization debate requires a great deal of additional research effort. However, researchers rarely agree, and even if they agree it is doubtful whether that would convince politicians to proceed with cannabis legalization. Conducting further research and hoping that an evidence-based cannabis policy will emerge is wishful thinking. Rather than muddling through for several decades it would be wise to start moving on the long and winding road to cannabis legalization. This would make life more comfortable for cannabis users, remove criminal organizations from the scene, allow for the possibility of quality control, provide governments with tax revenues and make it possible for researchers to collect empirical evidence. In short, it is time for politicians to walk down the legalization road ‘to boldly go where no man has gone before’.


  1. Top of page
  2. Declaration of interests
  3. References
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