VoxEU Column Health Economics

Is cannabis use really so harmful?

There is a robust positive association between support for cannabis liberalisation and cannabis use, but it is unclear whether users have discovered that cannabis is innocuous, or if these types are inherently more liberal regarding drug policy. This column exploits variations in opinion between current and former cannabis users to work towards establishing causality. Results suggest that supporters of liberalisation are speaking from experience rather than personal interest.

Cannabis is prohibited in many countries. The European Monitoring Centre for Drugs and Drug Addiction (2013) discusses several alternatives to prohibition, varying from decriminalisation to regulation and legalisation.

  • Decriminalisation refers to the removal of the criminal status for personal possession or use.
  • Regulation concerns limits to access and restrictions on advertising.
  • Legalisation refers to cannabis use and supply, making lawful what previously was prohibited.

Legalisation mainly refers to removal of all criminal and non-criminal sanctions and is generally used in the context of cannabis supply.

Although prohibition prevails in the world, some countries are becoming more tolerant. The Netherlands quasi-legalised cannabis use through the introduction of ‘coffeeshops’ which are licensed cannabis sales outlets.1  Recently, citizens in two US states – Washington and Colorado – voted in favour of a state licensing system for production and supply of cannabis to retail outlets. The system was introduced on 1 January 2014 and more US states are expected to follow. In Uruguay a licensed production and retail system for cannabis will be introduced soon.2  A brief overview of the legal framework regarding cannabis in these three countries is given in Table 1.

Table 1. Overview of cannabis laws in the Netherlands, US and Uruguay

Source: European Monitoring Centre for Drugs and Drug Addiction.

When it comes to policy debates about cannabis legalisation, there are frequent references to adverse effects of cannabis use on physical and mental health as well as several life outcomes such as educational attainment and labour market position. In our recent overview study on the effects of cannabis use, we conclude that there do not appear to be serious harmful health effects of moderate cannabis use, but there is evidence of reduced mental well-being for heavy users who are susceptible to mental health problems (Van Ours and Williams 2014). Furthermore, while there is robust evidence that early cannabis use reduces educational attainment, there remains substantial uncertainty as to whether using cannabis has adverse labour market effects.

It is important to assess how severe the adverse effects of cannabis use are, but this is easier said than done. We argue that analysing the determinants of opinions on the legalisation of cannabis might help to investigate individual assessment of the harmful effects of cannabis use. Differences in opinions on cannabis laws between non-users, current users and past users of cannabis can be informative about potential dangers of cannabis use and how these dangers are assessed by individuals.

It is well-known that cannabis users are more in favour of legalisation than non-users. This is confirmed in a European study on youth attitudes toward drugs (European Commission 2011). Individuals aged 15-24 years in the 27 EU countries were asked to report their opinions on specific cannabis policies. On average, 60% of the youngsters think that cannabis use should be banned, while 40% think it should be legalised (with or without restrictions). Figure 1 shows that in EU countries where the percentage of youngsters who ever used cannabis is high, the support for legalisation of cannabis use is also high. The graph also shows the situation in the US, where among youngsters of 18-29 years, 36% have tried cannabis and 69% think that cannabis use should be legalised. In terms of the combination of cannabis use and opinions on legalisation, the US and the Netherlands are not very different.

Figure 1. Percentage of those who support a policy of cannabis regulation and percentage having ever used cannabis among youngsters in 27 EU countries and the US

Source: European Commission (2011) - youngsters: 15-24 years; USA: 2013; youngsters: 18-29 years.

Figure 1 is based on cross-country averages and serves a descriptive purpose. Nevertheless, more detailed studies have also found that cannabis users are more in favour of legalising cannabis and less in favour of prohibition. According to a US study which used data collected in 1997 and 1998 in Houston, it appears that 68% of drug users were in favour of legalising cannabis, while only 33% of the non-drug users were in favour (Trevino and Richard 2002). A study from Norway performed in 1989 shows that 65% of cannabis users were in favour of cannabis prohibition while among non-users this figure was 95% (Skretting 1993). In the Netherlands in 2008, among cannabis users only 7% were in favour of prohibition of cannabis, while the figure was 50% among non-users (Van der Sar et al. 2011). In Australia in 1998, 57% of cannabis users were in favour of legalising cannabis while among the non-users this was only 18% (Williams et al. 2011).

All in all, several studies suggest that support for cannabis legalisation is higher among cannabis users. Of course this relationship does not imply a direction of causality. It could be that individuals who are more likely to consume cannabis are also more in favour of legalisation, without personal experience affecting opinions. Knowing whether or not there is a causal effect from cannabis use to opinions is interesting because if there is a causal effect, this reveals how potential dangers of cannabis use are assessed. If cannabis use has a favourable effect on opinions about legalisation, this implies that cannabis use is not as harmful as was originally believed. However, such a causal effect may also have to do with self-interest, with legalisation leading to easier access and perhaps lower prices. We argue that it is possible to make a distinction between inside information and self-interest by comparing how past and current cannabis use affect opinions. Whereas the effect of current cannabis use may be a mixture of self-interest and inside information, the effect of past cannabis use is related to inside information only.

Our analysis

We estimate the causal effects of current and past cannabis use on opinions about cannabis legalisation (Palali and Van Ours 2014). In the dataset used, respondents are asked to report their opinions on several different policy statements regarding cannabis in the Netherlands. Opinions are reported in a scale of one to five, with five indicating “definitely agree”. We focus on two policy statements: “Cannabis should be legalised”; and “It should be permitted to sell cannabis through coffeeshops”. The second statement refers to the current situation in the Netherlands, while the first statement implies a more liberal attitude to cannabis use.

In our analysis we take into account potential correlation in unobserved personal characteristics that affect both opinions and cannabis use, thus establishing whether there is a causal relation from cannabis use to opinions. Our results indicate that both current users and past users are more in favour of legalisation. The opinions of current users are expected to be affected by both self-interest and information, whereas the opinions of past users are no longer affected by self-interest. Thus, for past users the effect stems from the information about cannabis use. The fact that past use predicts more liberal views about cannabis laws indicates that cannabis may not be as harmful as they originally thought, or as non-users are inclined to think. Past users of cannabis – knowing about cannabis use more than those who have never used, or “never-users” – are more likely to support liberal policies.

Using our estimation results we calculate the estimated effects of current and past cannabis use on opinions about cannabis policies. Row (1) of Table 1 below shows the results of these calculations. The numbers in the table are constructed by first simulating the probabilities for each alternative in the ordered responses given to policy statements for never-users, current users and past users. For simplicity we merge the categories of “definitely agree” and “agree” and the categories of “definitely disagree” and “disagree”. Then we calculate the differences between probabilities corresponding to a cannabis user and a never-user. Therefore the numbers in the first column, for example, show how much more cannabis users disagree with the given policy statement (or how much less if negative). Similarly the third column shows how much more cannabis users agree with the given statement. All in all, simulations show that there is a considerable difference in opinions on cannabis legalisation between never-users and users. Current cannabis users are systematically more in favour of legalisation. Although less so than current users, past users are also more in favour of legalisation compared to never-users. Row (2) reaffirms these findings on a similar policy statement about cannabis legalisation.

Table 2. Estimated differences in percentage of people who agree to the given statement

In order to investigate whether the results obtained for the statements about cannabis legalisation are driven by some unobserved confounding factors, we perform several placebo/falsification analyses using opinions about different policy statements unrelated to cannabis use. Rows (3) and (4) in Table 1 show the results of simulation for opinions about alcohol restrictions. The first opinion statement is “There should not be happy hours in bars and discos.” The second statement is “No alcohol should be sold to those under 16.” For neither of these statements do we find an evidence of a substantial difference between never-users and users. However, cannabis and alcohol can be complementary, or even substitutes. Therefore rows (5) and (6) present the same simulation results for two policy statements that are completely unrelated to substance use. In row (5), we use information about opinions on “The state should no longer give students a study grant but only a study loan under favourable conditions". There is no substantial effect of cannabis use on opinions. In row (6), we use information about opinions on “Citizens should have more influence on government policies”. Again there is no effect of cannabis use. It is not the case that cannabis users and non-users are systematically different in their opinions about government policies in general; the difference exists only if the policy is about cannabis legalisation or restrictions on cannabis.

Concluding remarks

In short, we investigate the determinants of the support for cannabis legalisation, finding a causal effect of personal experience with cannabis. Current and past cannabis users are more in favour of legalisation. We relate this to self-interest and inside information about potential dangers of cannabis use.

While the effects of self-interest are not very surprising, the effect of inside information suggests that cannabis use may not be as harmful as cannabis users originally thought it was and not as harmful as non-users are inclined to think it is.


European Commission (2011), Youth Attitudes on Drugs: Analytical Report, European Commission, Luxembourg.

European Monitoring Center for Drugs and Drug Addiction (2013), Models for the legal supply of cannabis: recent developments, Lisbon.

Palali, A. and J. C. van Ours (2013), “Distance to cannabis-shops and age of onset of cannabis use”, CEPR Discussion Paper 9632.

Palali, A. and J.C. van Ours (2014), “Cannabis use and support for cannabis legalization”, CEPR Discussion Paper 9944.

Skretting, A. (1993), “Attitude of the Norwegian population to drug policy and drug-offences”, Addiction 88, 125–131.

Trevino, R. A. and A. J. Richard (2002), “Attitudes towards drug legalization among drug users”, American Journal of Drug and Alcohol Abuse, 28(1), 91–108.

Van der Sar, R., E. Brouwers, L. van de Goor, and H. Garretsen (2011), “The opinion on Dutch cannabis policy measures: A cross-sectional survey”, Drugs: education, prevention and policy 18(3), 161–171.

Van Ours, J. C. and J. Williams (2014), “Cannabis use and its effects on health, education and labour market success”, CentER Discussion Paper 2014-24.

1 See Palali and van Ours (2013) for a brief history of cannabis policies in the Netherlands.
2 In December 2013, the president of Uruguay signed a government bill that legalised cannabis. Although the details of the regulation on production and retail still have to be established, citizens can grow their own cannabis.
Williams, J., J. C. van Ours, and M. Grossman (2011), “Why do some people want to legalize cannabis use?”, CEPR Discussion Paper 8228.

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