Can phenergan (promethazine) cause sexual dysfunction?

Yes: Not a prominent side effect , but it's structurally similar to some of the older antipsychotics, has small effects on dopamine, and thereby a negative effect.

Maybe: Many medications have been associated with sexual dysfunction in men and women. However it is difficult to prove. From an individual perspective the best way to tell is to see if symptoms worsen with starting the medication and improve when discontinued. This should be done under your doctor's direction for prescription drugs and those OTC meds that may be risky to stop (i.e. aspirin).