My friends is taking 2 to 3 grams of cocaine daily from 6 months. When & what will be the side effect on his brain and body in the long run?

Yes, death. I agree with dr. Villaplana that extended use of Cocaine like this does lead to death. Until that point, some effects you & your friend might want to know about include abdominal pain and nausea, irregular heart beat, heart attack, chest pain, respiratory failure, stroke, seizures and headaches. So while the drug may bring euphoria, it also comes with scarier things.