Makers of drugs that were quickly approved by the Food and Drug Administration took longer to conduct follow-up studies to confirm that the drugs were safe and effective than pharmaceuticals approved through the normal process, according to a new study.

The study looked at mandated trials of drugs after they were cleared through accelerated approval from 2009 to 2013. The FDA gave accelerated approval to 22 drugs for 24 sicknesses — 19 of which were for cancer — according to the study published in the Journal of the American Medical Association on Wednesday.