Now that President Trump has declared the opioid epidemic a public health emergency, it’s useful to examine the full extent of its causes. Some — doctors overprescribing opioids, pharmaceutical and insurance companies trying to maximize profits — are well known. But a growing body of research examines the powerful part socioeconomic forces play in the epidemic. The Commonwealth Fund’s David Blumenthal, M.D., and Shanoor Seervai explain in Harvard Business Review.