Half of all drugs that received accelerated approval by the FDA from 2009-2013 failed to complete required post-approval studies within three years of going on the market, according to a study published Tuesday in JAMA. Another study, also in JAMA, found that less than half of all high-risk medical device modifications underwent rigorous testing before entering the market.

Since 1992, drugs that treat serious illnesses have had the option of fast-tracking their FDA approval. Instead of completing rigorous clinical trials that can take years, the FDA would allow companies to put promising drugs on the market on the condition that they continue to conduct studies that prove that the drugs actually work.

What they did: The first study looked at 38 trials for 22 drugs, and found that only 19 of those trials were completed within three years. The ones that were finished were frequently not as rigorous as the studies that would have been required had the drug been approved via normal channels. There was also evidence of missing or lost data and selection bias.

It's not all bad, notes STAT's Damien Garde, who writes that a study published this week in Health Affairs concludes "that the agency is consistently singling out the most promising therapies [for] speedy review."