Just tell him something like this...."Dad listen...im really sorry and if you dont trust me for awhile i understand...thats fine...but i just dont want you to be dissapointed or ashamed....im really sorry my friends said it was fun and wasnt really and drug since its a medicine and they said it wasnt harmful or anything just something fun to do ...so i did it and i compltely screwed up and i know i shouldnt listen to what my friends had to say or anything but i was stupid and did im sorry dad just please try and forgive me...im sorry and i love you.." say something like that ...it might help