Can one please show me or tell me which retin-a gel should i use for blackheads ? and what are its side effects ? does it dries the skin ?

Start with cream: Since the cream is less drying than the gel, unless your face is very oily i would start with that first. You can in the beginning use it every other night and then use it nightly. Everyone has to go through a period of time when their skin is dry. This is normal and cold the period of retinization. It will disappear with time.