What Are The Side Effects Of Long Term Use Of Dexpoten Syrup For Flu?

I am a patient of asthma. I took preventive drugs for long. After recovering from asthma, I started smoking under depression. Smoking caused some nasal congestion and flu. In order to get rid of this nasal congestion and flu, I started taking Dexpoten syrup. I am taking this syrup for almost last six years besides smoking. I have gained 20 k.g and my face skin color is getting dark day-by-day. I look older than I am. I do not feel good while taking stairs and moving heavy objects. I want to quit this Dexpoten syrup. How can I do this?