Greater Danbury area Police Departments are participating in the  Drug Enforcement Administration's National Prescription Drug Take Back Day on Saturday.  Most will have drop off boxes in their lobbies from 10am to 2pm, no questions asked.  The collection is held nationwide twice a year.  In April, about 44-hundred law enforcement agencies participated.  420 tons, about 839-thousand pounds of  expired, unused or unwanted over-the-counter and prescription medications were collected.