Most of the currently used anxiolytic agents act via gaba or serotonin. The latter include drugs traditionally classified as antidepressants, which are reviewed in the next chapter. This chapter reviews the results of ten experimental studies investigating the effects of anxiolytics on driving performance using over-the-road tests. Results show that only the serotonergic drugs (buspirone, ondansetron and ritanserin) had a low potential for impairment. All gaba-agonists (diazepam, lorazepam, oxazepam, clorazepate, alprazolam, alpidem, suriclone) had moderate to severely impairing effects on driving in the doses studied. Impairment was clearly dose dependent, and increased on average with increasing blood concentrations. However, most studies analyzing correlations between drug concentrations in plasma and effects on driving performance found low and non-significant correlations, indicating that prediction of impairment from blood concentrations is problematic.furthermore, tolerance was found to develop only very slowly, and impairing effects did not seem to be counteracted by improvement in anxiety symptoms. Finally, subjects seemed relatively unaware of the effects of the drugs. Awareness of these effects was only seen with severe objective impairment, indicating that patients should be warned explicitly about the risks associated with using these drugs by their physicians or pharmacists.keywordswklv vwxgdvvrfldwhg zlwkohvv wkdqkljkhu wkdqlqglfdwhv wkdwthese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.