Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?

Yes, friends can influence for taking alcohol or drugs. Following measures can be taken :

a) Avoiding undue peer pressure.

b) Not taking undue pressure of failures beyond its threshold.

c) Getting counselling from some counsellor.

d) Seeking help from parents and peers.

e) Seeking medical help.