I am a student should I choose metric or o levels?

I want to b a doctor but I am confused to choose metric or o levels ? are marks cut in the o levels exam ? is o levels preferred for medical ? is o level an international studies ? do we need to go abroad for studies if we choose o levels ? please reply it is about my future my teachers says that I can do o levels but for medical it is better to choose metric . THANKS IN ADVANCE ! AND PLEASE REPLY ME ON MY YAHOO ID : [email protected]