Hi dear SAS-Lers,   I have encountered a coding problem and would like to know whether anyone on the list could help me.   My goal is to find patients who are concurrently taking 3 or more medications(different drug names) over a 6 month time period in 2010.  I need to look at the fill date along with the days supply to determine if there is any overlap between at least 3 different med scripts in a continuous 6 month period for a given patient. The following is the example data, any help would be highly appreciated!   Mem_id      Fill_date            Drug Name                             Days_supply 1B         15FEB2010       GLYBURIDE-METFORMIN HCL            90 1B         17MAY2010      GLYBURIDE-METFORMIN HCL            90 1B         17JUN2010        ACTOPLUS MET                                90 1B         17JUN2010       JANUMET                                           90 1B          07JUL2010       ACTOPLUS MET                                90 1B         02NOV2010      GLYBURIDE-METFORMIN HCL            90 2B         17JUN2010       JANUMET                                           90 2B          07JUL2010       ACTOPLUS MET                                90 2B         02NOV2010      GLYBURIDE-METFORMIN HCL            90 3B         15FEB2010       GLYBURIDE-METFORMIN HCL            90 3B         17MAY2010      GLYBURIDE-METFORMIN HCL            90 3B         17JUN2010        ACTOPLUS MET                                90   Thanks! Nancy