Three general strategies exist for projecting the likely consequences of a change in the legal regime for drugs: (1) draw on existing theory and research; (2) conduct demonstration experiments or quasiexperimental program evaluations; and (3) project the effects of decriminalizing or legalizing drugs on the basis of analogies to experiences of other places, historical periods, substances, or behaviors. The Dutch experience with marijuana illustrates strengths and limitations of reasoning by analogy. While the Dutch case and other analogies have flaws, they appear to converge in suggesting that reductions in criminal penalties have limited effects on drug use, at least for marijuana, but that commercial access is associated with growth in the drug-using population. The prevalence of marijuana use in the Netherlands, Denmark, Germany, Norway, and the United States is discussed. 53 references, 2 tables, and 1 figure