Should I go to a party, if i know there will be drugs and alcohol?

Okay right so I am a 14 year old boy (15 in a month) and I was invited to a friends house for a party on her birthday. I was told there will be alcohol there, which I am not too bothered by because I have had alcohol before and it's not anything that I crave upon, however I feel my friends might pressure me into getting drunk. There will also be drugs involved, weed. I am a bit reluctant to go now, because most of them smoke weed on a regular basis. I feel that they will pressure me, I don't want to say no because its my friends birthday, she wont do anything, she was caught before by her mum and said she will never risk it again, and to be honest i wouldn't let her do it. I don't know what to do, should I go or not???