From an article in the July 25-31 issue of The Economist:

Are Americans consuming fewer drugs? Probably not. A dramatic drop in the latest estimate of the quantity of illicit drugs consumed and produced in the United States may confirm only that nobody really knows.

For the past 10 years an inter-agency committee, the National Narcotics Intelligence Consumers Committee, has published an annual estimate. It has always been a bit of a mystery how this estimate was prepared, but the figures, from year to year, were at least consistent. Now, suddenly, in the committee's latest report, they are not. Cocaine consumption for 1985 is estimated at 73 tons, compared with 130 tons in 1984; marijuana consumption for 1985 is estimated at 4,900 tons, compared with 8,500 tons in 1984. . . .

The new lower estimates appear to be based on the household surveys carried out by the National Institute on Drug Abuse. The surveys provide a good estimate of trends but underestimate both the number of takers and the amount they take. They miss groups that do not live in households, such as college students and soldiers on military bases. Even so, they provide the only available "hard numbers" on drug taking.

Other estimates involve subjective guesses. Moreover, different agencies have different interests; their guesses often differ. The State Department, for instance, would like a low estimate for the share of marijuana produced domestically; high estimates reduce the moral authority of the United States in its attempts to deter Latin American suppliers. The domestic supply-busting agencies, on the other hand, may have an interest in a high estimate of the home-produced share, since this makes their efforts look better.