How does the FBI determine if you're disqualified from buying a gun due to drug addiction?

Does anybody know how the disqualifying event of drug addiction/abuse is determined during a background check?I'm 45 years old and have never been caught or arrested for drug use, selling, or anything drug related. As a Cancer patient since 2009 I did develop an addiction to pain meds following a series of surgeries to remove Cancerous tumors.I'm hoping disqualification is based on drug-related arrests and/or convictions (which I have none), and not just a doctor's note in my medical records saying I was addicted to pain meds for a short period of time. via /r/CCW https://ift.tt/2DaVDzG