Before any medication reaches the drug store it's got to be approved by the FDA. And some drugs are approved faster than others.
"It's important to understand how well-studied new drugs are at the time of approval," said Dr. Nicholas Downing, Yale University School of Medicine.
So Dr. Downing and his colleagues wanted to find out what's behind the approval process. Not all drugs go through the same type of review. There are various factors that go into drug trials, and they can be different depending on the type of drug or manufacturer.
Researchers looked at criteria publicly available on the FDA website. Besides the ultimate outcomes, the information included how many trials were involved, how long the trials lasted and how many patients were studied.
"We uncovered there being much more flexibility in what the FDA requires of manufacturers," said Dr. Joseph Ross, Yale University School of Medicine.
There were some findings that raised safety questions. For example: expedited drugs took about five years of clinical testing, versus seven and a half years for drugs with a standard review.
And researchers also found that fewer than half the drugs specified for long-term use are studied for more than six months. But experts say this means much-needed drugs will come to market sooner.
"The FDA is doing a good job of maintaining these flexible approval standards and tailoring each approval appropriately," said Ross. "So we can have these flexible standards that allow shorter trials and less-certain trials to go forward and to be the basis of an FDA approval, so long as we are continuing to study these medications in the post-market period."
However, critics say the FDA hasn't done enough to put safety measure in place for all drug approvals, and that much needs to be done in making the process more consistent.
In a statement, the FDA said it will review the study in the Journal of the American Medical Association but says the findings show expedited development programs are working by getting promising new drugs to patients more quickly.