I Was Given A Script Quit Some Time Ago For

i was given a script quit some time ago for back pain, the medication was Narco. It was ordered PRN so as i stopped needing them for my back , i quit taking them but had alot left in the original bottle. im now on a color code drug screening program for the court. how old can a script be and still be ok to take beings it was in fact My script that i just kept in my medicine cabinet?? my back went out again and without thinking it mite be to old i took them for my pain to save the money of seeing the doctor for the exact same injury.