Is it safe to take promethazine hydrochloride (phenergan) if you have asthma?

No: Since there are other ways to handle the symptoms that Phenergan (promethazine) is prescribed for, the dangers far outweigh the benefits imho. If your doctor has prescribed it knowing about your asthma, ask why it seemed like a good idea. If the reasons make sense, it might be worth considering, but i doubt it - especially if your asthma is more than mild. Good luck!

Maybe: Promethazine suppresses a cough. Sometimes it is important to cough so mucus comes off your chest. Other times it is important to get some sleep so Promethazine may be needed, especially if it is used for only a short time. It may suppress a cough and reduce irritation in your throat so you are less likely to cough again.