For the second year in a row, the percentage of American workers testing positive for illegal drugs has increased, according to a study conducted by Quest Diagnostics. Quest Diagnostics’ Drug Testing Index (DTI) – an annual analysis of workplace drug testing trends – found that the number of employees in the general workforce testing positive for illegal drug use increased in 2014 to 4.7%, up 9.3% from the year prior. Prior to 2013, DTI had shown a decade’s-long decline in employees’ use of illegal drugs. The increase in 2013 was driven largely by a 20% jump in the number of employees testing positive for marijuana use in Colorado and Washington. While marijuana remains the most commonly detected illegal drug, the number of employees testing positive for cocaine, methamphetamines and heroin also increased.