There is growing concern around the world about drug use and road safety. Drinking alcohol and driving is a well studied risk factor for road traffic crashes, injuries and deaths but drug-induced impairment of driving is causing increasing concern in many countries around the world. For many years there have been several gaps in our knowledge, particularly about the global extent of the problem, the relationship between drug concentrations and crash risk, appropriate threshold limits in blood, legislation and enforcement of effective measures to prevent drug-driving. However, these knowledge gaps are progressively being filled by a growing body of evidence on drug use and road safety, including effective ways to reduce drug-induced road traffic crashes and injuries.