Side effects of generic competition?

This study examined the relationship between generic drug market shares and the number of reported side effects. Yearly time-series data for the number of reported side effects and information on market shares, prices, and quantities from 1972 to 1996 were used in this study. Poisson and negative binomial regression models were used in the statistical analysis. The results show that increased generic market share increases the number of reported side effects for all estimated models. When studying the relationship at the substance level, increasing generic market shares increases the number of side effects for 7 of the 15 substances. Generic substitution laws and measures to increase generic competition may thus have unintended consequences since these results show a positive relationship between generic market shares and reported side effects.