This exploratory study investigates major changes in opioid substitution treatment during the last decade in Austria and identifies main interests groups and their interplay. Different levels of visibility of interest groups and variations in latency of interests contribute further to the complexity of the multilevel structure of interests and interest groups regarding substitute therapy issues. Austria's unique low threshold of substitution treatment was developed during the 1990s, and is based on the prescription of slow release morphine and on the high involvement of GPs. Opponents, becoming active during the new millennium, succeeded in tightening up legal regulations but failed to change treatment practice.