Problems in the measurement of psychotropic drug consumption.

Two problems of measuring psychotropic drug use are described and illustrated using sales of psychotropic drugs in Finland and Norway. Classifying psychotropic drugs is a problem because the meaning of psychotropic drugs is not clear on a theoretical or practical level. In particular, the role of hidden psychotropic drugs--psychotropics included in combination products--is noted. Previous studies comparing the Nordic countries did not include combination products. Because a notable proportion of psychotropic substances sold in Finland were combination products, the inclusion of hidden psychotropic drugs affected the comparative levels of psychotropic drug use in Norway and Finland. Another problem in measuring psychotropic drug use is the unit of measurement. Traditional units of measurement, including defined daily dose (DDD), are discussed, and a new unit called the defined exposure dose (DED) is introduced. DED estimates the potential chemical exposure of the population to drugs. Sales of psychotropics in numbers of DDD/ and DED/ 1000 inhabitants/day in Finland and Norway from 1962 to 1978 were compared. Sales appeared to be much higher when DEDs were used. Irrespective of the unit used, sales were greater in Finland than Norway. Methods used to measure psychotropic drug use can affect conclusions drawn. The choice of unit of measurement should depend on the problem being studied, data source, and available resources. The concept of DED merits further investigation.