The continuing demand for measures of the size of global drug revenues has produced a supply of numbers that consistently overstate international financial flows. This paper shows that, rather than $500 billion, the annual figure in trade terms may be about $25 billion. As with many refined agricultural products, most of the revenues go to distributors rather than to primary producing countries. The authors explore the need for estimates of the global drug markets, address the difficulties of obtaining ‘good’ numbers, and describe opportunities for developing better estimates of flows and revenues. There are at least three reasons for caring about the numbers: they can help to improve understanding of the drug production and consumption problem and identify appropriate policy responses.