If you are being tested for drugs at work or sports, then just tell the tester that you have ingested Phenergan  (and have proof if needed, as this is a prescribed drug).  If the phenergan gives a "false positive" for THC (active ingredient in marijuana)   metabolites, then you are protected from any repercussions. If you are remiss in reporting this you can lose your job, get sanctions, or need to have another test. THC remains inthe system for appr. 30 days. I doubt if phenergan has the same half-life. Either way save yourself trouble and list all medications you have taken over the past 30 days prior to the drug test.