We read with interest MacCoun & Reuter's (Reference Maccoun and Reuter2001) report on evaluating alternative cannabis regimes. In The Netherlands, drug policy is a topic of great interest. A scientific evaluation of policy regimes would be highly appreciated. MacCoun & Reuter's paper illustrates that this, however, is not an easy job.

As the authors stress, cross-national scientific evaluations are hampered by a lack of comparability due to methodological differences. Nevertheless, many studies summarised in their Table 1 are not methodologically comparable. MacCoun & Reuter compare the results of Dutch school surveys with those of population surveys in the USA. However, school surveys yield higher prevalence figures of substance use than population surveys do (Reference Gfroerer, Wright and KopsteinGfroerer et al, 1997). Furthermore, the age group “approximately 18” from the Dutch school survey is compared with the 18-year-old age group in the American national study. In The Netherlands schooling is compulsory until the age of 15-16 years, so 18-year-old high school students cannot be considered as representative of all 18-year-olds in our country. Among high school students aged 12-18 years we saw an increase in cannabis use in 1984-1996, but this had stabilised in 1999. The arguments that the rise may be associated with the coffee shop model and with a phenomenon the authors describe in terms of commercialisation and glamorisation do not quite convince us.

1. (a) The increase in cannabis prevalence coincides with a supposed increase in the number of coffee shops but this does not prove a causal relationship.

2. (b) About 80% of Dutch municipalities have no coffee shops at all (Reference Bieleman and GoereeBieleman & Goeree, 2000). Less than half of cannabis consumers purchase the drug in a coffee shop — the majority obtains it elsewhere (from a friend, a private house, sale on the street, courier services and take-away services).

3. (c) The authors do not present clear definitions of the concepts commercialisation and glamorisation. Coffee shops must adhere to the so-called AHOJ-G criteria, which include no advertising. The Public Prosecution Department proclaimed deviation from these criteria a nationwide criminal prosecution policy in 1991.

4. (d) The increase in cannabis use in the USA seems to have taken place much earlier than in Europe. The authors do not offer a plausible explanation for this trend but indicate the importance of non-policy factors.

5. (e) Countries with a high prevalence of drug use are more likely to experience a downward trend than countries with low prevalence figures. This is now the case in Europe: an ongoing increase in countries with previously low use levels, and stabilisation or even decline in countries with previous high prevalence figures, both in general population studies and in school surveys, confirm the tendency towards convergence (European Monitoring Centre for Drugs and Drug Addiction, 2000; Reference Hibell, Andersson and AhlströmHibell et al, 2000). In the UK cannabis use among students was significantly lower in 1999 than in 1995, while in France cannabis prevalence increased steeply, although there are no coffee shops in France. In The Netherlands, among students between 1996 and 1999, not only cannabis use but also use of ecstasy, cocaine, heroin and amphetamines stabilised (Reference de Zwart, Monshouwer and Smitde Zwart et al, 2000).

Clearly, trends in drug use are influenced by a complex interplay of factors.