In divvying up U.S. spending on orphan vs. nonorphan indications for drugs approved for both, a new study could fuel future debates and inform policy on orphan drug incentives. The study, led by a team of University of Michigan and Boston University researchers, found that 21% of the total dollars spent in 2018 in the U.S. on the 15 top-selling partial orphan drugs went to the treatment of rare diseases, while more than 70% went to the treatment of common diseases.