If you are injured on-the-job, your Employer is entitled to have you drug tested. However, it is not necessarily the end of your claim if you test positive. The drug-use must have caused or contributed to the accident.
The question is: Did the drugs in your system cause you to be less attentive, more-clumsy or somehow cause or contribute to your work-accident. However, that is not always the case.
For example, if a board falls from above onto your head and you never saw it, did your drug use cause or contribute to that incident? Would the accident have occurred regardless of your drug-use? But, if you were slow to react and avoid the falling board because you were under the influence, then that is an issue and you can be denied benefits. Or, if you routinely smoke marijuana and have for years, did the remnants of the drug in your system really affect you given how often you smoke? You may have built up a tolerance.
Consult an experienced attorney who specializes in workers’ compensation if you fail a post-accident drug-screen.