Will promethazine come up on a drug test?
Most drug tests simply test for illegal drugs, opiates, amphetamines, and benzodiazapenes. Promethazine (Phenergan) does not fall into any of these categories. It is a anti-nausea medication that only works on the stomach itself, and does not contain any substance tested for in drug tests. However, because promethazine can make you very sleepy, it is not advised to take it during work or when driving.
I am not a doctor but I do have experience with UA's and promethazine or as it is commonly referred to as Phenergan has nothing in common with cocaine so in my opinion it is very unlikely for Phenergan to give a false positive for cocaine. It is much more likely if you did come up with a false positive that the test is simply bad and wrong This has happened to me.