The author reviewed the evidence regarding the effects of liberal and repressive policies on the prevalence of drug use in the various countries. He first reviewed the relevance of supply and demand factors and the role of the law in deterring people from drug use. He then analyzed the effects of policy changes and variations in a cross-national perspective. The data relevant to this study were not readily available, however, because demand and supply factors have not usually been monitored when policy changes have been implemented. The cross-national surveys done by the European Union as part of the Eurobarometer surveys have performed poorly regarding drug use and attitudes toward drug use in Europe; nonetheless, there are some data, also on a comparative basis, that allow some tentative conclusions. These are data that can be drawn together from various sources and are roughly comparable in quality. The comparison between the Netherlands, which has liberal constraints on drug use, and other countries suggests that opportunity for drug use based on availability and accessibility are not as significant as demand factors in determining the prevalence of drug use in a country. Socio-cultural attitudes, living conditions, and attitudes toward drugs in the population apparently impact the level of drug use more than the threat of punishment. Liberal drug policies do not necessarily increase drug use. Even de facto legalization coupled with high availability as in the Netherlands does not necessarily promote drug use. Repressive polices, on the other hand, do not guarantee low drug usage. Such policies may have an impact on supply, but compared to demand, the effect is negligible. Interventions and punishments applied to the drug user might increase his/her willingness to engage in delinquent behavior rather than reduce it. This could be due to the user turning to drug-using friends for support and thereby stabilizing drug use. Drug-using friends constitute the most important factor in explaining drug use. Demand for drugs, especially hard drugs, might be linked more to the general socioeconomic situation of the country rather than to the prevailing drug policy. Neither the level of soft drug use nor the drug policy explains why some countries have high rates of drug use while others have low rates. Thus, formal norms set by the law and official policy might be negligible in influencing drug-using behavior compared with the informal behavioral norms of the population. Research is needed to examine in greater detail the interplay between attitude, demand, drug supply, and drug policy. 1 table, 1 figure, and 58 references