Rates are aggregated at the ZIP code level. Overdose rates are categorized with reference to state (15.4 deaths/ 100,000 residents) and national (10.4 deaths/ 100,000 residents) overdose rates. The lightest reds represent ZIP codes with fatal overdose rates lower than that national average, whereas the darkest red accounts for rates higher than the national and Massachusetts state average. Town/city boundaries are outlined in black. A) 2011; B) 2012; C) 2013; D) 2014; E) 2015; F) Aggregated/average annual fatal overdose rate per 100,000 Massachusetts residents, 2011–2015.