This article examines the tensions within the international drug control system which are putting the until now consensual position in regard to the prohibition on drugs supply and use for anything other than medical and scientific use – the Vienna Consensus – under strain. The article examines a number of areas where policy stress is leading to controversy about potential violation of international drug control treaty obligations by states parties. Drawing a comparison with earlier periods of stress when drug control fell under the League of Nations, it suggests that what appears to be occurring is a shift in the Vienna consensus, and that the drug conventions are sufficiently flexible to permit resulting shifts in practice, although reform would be preferable.