To the Editor In our study of the costs of drug development published in JAMA, we used clinical trial success rates to account for the costs of failed trials. We sourced these rates from a previous study. We recently became aware that the authors of that study issued a correction to the aggregate phase 2 success rate reported in their article. Initially, they reported that 35.1% of drugs that enter phase 2 clinical testing are ultimately approved by the US Food and Drug Administration, whereas the corrected percentage is 21.0%. Because we based our analysis on the initial figure (35.1%), we have now updated our analysis using the corrected data of 21.0%.