You were given what is typically referred to as "diversion". You most likely appeared in court, pled quilty to the charge and received an alternative sentence (enrolling in a substance abuse program). In most cases, upon successful completion the charge is withdrawn and your record is cleared. As a general rule this happens automatically; in some cases you need to file for expungement or sealing of your record afterward. The process for all of this varies from state-to-state. At this point you should get a copy of your criminal history record (i.e. rap sheet) to see just what does show up. You can get a copy through your state (google for information or contact the state police for help). If you do have to get an expungment, while you can do this yourself, you may want to consult with a criminal law attorney.