Driving under the influence of drugs - The failed quest of finding medical signs indicative to driving impairment.

Motor vehicle accidents (MVA) are the leading cause of death in childhood and young adult age. One of the most important factors behind MVA is driving under the influence of alcohol (DUIA) and drugs (DUID). The importance of DUID is rising together with the increasing drug abuse. The legal approaches to DUID are based on impairment, impairment per se or zero tolerance. In case of impairment, the negative effect of the substance on the driving abilities has to be proven by a forensic expert, which can be challenging. This study compares the medical signs registered during blood sampling with the concentrations of substances detected by toxicological examination to find medical signs indicative of impairment. Statistical analysis did not find a correlation between substance concentration and measured parameters (pupil diameter, blood pressure and pulse rate). No connection was found between substance concentrations and the appearance of medical signs. The results indicate that pupil dilation, heart rate, and blood pressure could not be used as indicators of possible driving impairment by drugs, and no medical sign could reliably indicate the driving impairment by substances other than ethanol.