The Red Flag system at healthcare institutions, including pharmacies, is an online system that tells the institution information about your previous prescriptions. The system usually monitors the frequency with which you purchase a certain type of medication as well as the dosage. Although it is argued to be a breach of a person's privacy, the Red Flag system can be used to catch prescription drug abusers and medical identity theft. Pharmacies are allowed to deny purchases if they feel the person is buying too much of the same prescribed medication.
Look into your medical history. If you take a prescribed set of drugs each month or have given personal information to a pharmacy, chances are higher that you are Red Flagged.
Go to a reputable pharmacy and ask for a dosage of your regular prescribed medication. If you get the medication monthly, go before your regularly scheduled visit. This will increase your chances of finding out whether or not you are flagged.
If the pharmacist denies you the medication, then you are Red Flagged, as they would have to consult an online system that tracks when your next dosage should be given.