Today it appears that a general consensus exists concerning the methodological principles to be used in establishing the efficacy profile of a new drug in anxiety disorders, ie a double-blind, parallel group design testing different doses of the new drug versus placebo (Angst et al, 1993; Rickels, 1990), however there is also growing concern about increasingly high placebo response rates and important differences between countries in these trials. This seems to be true despite the fact that in recent years, selection criteria for diagnosis and severity of the disorders have become more clearly defined and more restrictive than in the past.

This situation increases the risk of false negative results in otherwise well designed clinical trials with new anxiolytic drugs and can incite pharmaceutical companies to abandon the further development of efficacious compounds even if they have potential advantages in terms of safety over the available products.