Positive Cannabis Drug Tests Not Associated With Increased Risk of Workplace Accidents
The use of cannabis is not positively associated with workplace accidents, according to a study published online in the Journal of Addictive Diseases. 
For the study, researchers assessed whether there exists a statistical association between cannabis use and work related accidents; they did this by “comparing the proportion of marijuana positive urine specimens for post-accident verses random samples” from five states (Indiana, Ohio, Pennsylvania, Kentucky and Missouri).
“This study failed to demonstrate a statistically significant difference between the numbers of laboratory positive marijuana urine drug tests for a group of random drug tests compared to a group of post-accident drug tests”, claims the study’s author.
“This study cannot be taken as definitive evidence of absence of an association between marijuana and work related accidents but the findings are compelling.”
A 2010 review of 20 years of published literature pertaining to cannabis drug testing and workplace performance came to a similar conclusion; “Urine tests have poor validity and low sensitivity to detect employees who represent a safety risk; … [and] urinalysis has not been shown to have a meaningful impact on job injury/accident rates.”
– TheJointBlog