Are drug prices subject to creative destruction? Evidence from the US, 1997-2017.

There are several types of pharmaceutical competition. In addition to competition among producers of the same chemical substance ("within-substance competition"), there may be competition among producers of different chemical substances in the same chemical subgroup ("between-substance competition"). There have been numerous econometric studies of the effect of within-substance competition on drug prices, but empirical evidence about the effect of between-substance competition is far more limited. The primary objective of this study is to assess the impact of the entry of new drugs in a drug's therapeutic class on branded drug prices, generic drug prices, and the generic market share, using publicly-available US data for the period 1997-2017. Two methods are used to estimate the effects of between-substance and within-substance competition on those variables. The first method is standard 2-way fixed effects estimation based on aggregate data. The second method, based on micro data, is estimation using the DID_MULTIPLEGT procedure developed by de Chaisemartin et al. (2021), which does not rely on, and allows us to test for, "parallel trends." Between-substance competition does not appear to have any effect on brand-name drug prices, although our inability to fully account for rebates may bias the estimates towards zero. (There is also little evidence for an effect of within-substance competition on brand-name drug prices.) However, between-substance competition has a significant negative effect on generic drug prices. We estimate that the 1985-2005 increase in the number of substances ever registered in a drug's ATC4 chemical subgroup reduced the 2017 price of generic drugs by 42%. (The ratio of the generic-price reduction attributable to rising between-substance competition to the generic-price reduction attributable to rising within-substance competition also happens to be 42%.) A striking finding is that the entry of imitators has no effect on the prices of brand-name drugs, but the entry of innovators has a significant negative effect on the prices of generic drugs in the same ATC4 chemical subgroup. In addition, between-substance competition has a significant positive effect on the generic market share: the 1985-2005 increase in the number of substances ever registered in a drug's ATC4 chemical subgroup increased the 2017 generic market share by 15.0 percentage points. Due to its effects on generic drug prices and the generic market share, the 1985-2005 increase in between-substance competition reduced the average 2017 price of drugs that were already sold in 1997 by 35%. We estimate that 36% of 2017 expenditure on drugs that were first registered during 1986-2005 was offset by reduced 2017 expenditure on drugs that were sold in both 1997 and 2017.