Background: The effects of drugs on driving performance should be checked with drug
concentration in the brain and at the same time with the evaluation of both the behavioural and neurophysiological
effects. The best accessible indicator of this information is the concentration of the
drug and/or metabolites in blood and, to a certain extent, oral fluid. We sought to review international
studies on correlation between blood and oral fluid drug concentrations, neurological correlates
and cognitive impairment in driving under the influence of drugs.
Methods: Relevant scientific articles were identified from PubMed, Cochrane Central, Scopus,
Web of Science, Science Direct, EMBASE up to April 2017.
Results: Up to 2010, no epidemiological studies were available on this matter and International
scientists suggested that even minimal amounts of parent drugs in blood and oral fluid could affect
driving impairment. More recently, epidemiological data, systematic reviews and meta-analysis on
drugged drivers allowed the suggestion of impairment concentration limits for the most common
illicit drugs. These values were obtained comparing driving disability induced by psychotropic
drugs with that of established blood alcohol limits. Differently from ethyl alcohol where both detection
methods and concentration limits have been well established even with inhomogeneity of
ranges within different countries, in case of drugs of abuse no official cut-offs have yet been established,
nor any standardized analytical protocols.
Conclusion: Multiple aspects of driving performance can be differently affected by illicit drugs,
and even if for few of them some dose/concentration dependent impairment has been reported, a
wider knowledge on concentration/impairment relationship is still missing.