Does phenergan (promethazine) depress your breathing ?

It's possible: Phenergan (promethazine) has been known to depress breathing in adults and this can be fatal in infants. It is a serious but rare reaction that can happen, so do not continue to take phenergan (promethazine) if you have noticed this, and contact your doctor so it can be noted in your chart. If you are having difficulty breathing, use your inhaler (if you have one). call emergency response if you are having difficulty.