You shouldn't do drugs on the job.
Lisa has been taking her opiate painkillers at an increasing rate and today she has work.
Lisa wants to do her job.
Lisa is in pain, but decides to wait until she gets home to take her pain medicine because it makes her foggy.
Lisa is in pain so takes some more opiate painkillers.
Lisa is able to perform her work tasks and keep up a professional appearance.
Lisa is obviously inebriated and her boss notices and fires her for being high on the job.