I am 30 year old man with no specific disease or medication.i take 25 mg viagra (sildenafil) in most of my intercourses. will it make adverse effect in long term?

Likely: No medication is without risk or side effect, and this class can be fatal, or lead to surgical emergency resulting in loss of erection function. If you are having erectile dysfunction at 30 years old you need evaluated by a urologist and possibly neurologist to identify problem that symptom is pointing to. Your age group is not highly common to need meds to assist.