Annual ADR report counts of opioid drugs are examined to develop a candidate index of overall safety of a drug. Actual counts for various drugs have been sourced from www.vigiaccess.org. A feature found to be common to all drugs considered is that an exponential function adequately describes the pattern of cumulative counts. In the exponential model, the parameter in the exponent (rate constant) is robust and remains the same whether counts are corrected for exposure or not. We propose use of this rate constant as adversity index of a drug. Drugs in use can be ranked by value of adversity index, lower value suggesting safer drug.