Thirty-two percent of the 222 new drugs — that’s almost one out of three — approved by the FDA from 2001 to 2010 were flagged for a safety issue roughly four years later, according to a new study.

The study defined safety issues as a withdrawal, boxed warning, or a safety communication. Many prescription opioid painkillers have a black box warning about their risk of abuse, addiction, and overdose, for example.

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The prevalence of safety issues post-approval isn’t necessarily a cause for concern, and could be seen as a bright spot for the FDA, according to Joseph Ross, the study’s lead author and an associate professor of medicine and public health at Yale University. “Some people look at one-in-three and get alarmed, everyone knows drug have both risks and benefits, to me it says that the FDA is doing its job,” he said, “it’s reevaluating therapies when they hit the market.”

Researchers found that drugs approved through the FDA’s accelerated approval pathway were more likely to report a safety issue following their approval. “The accelerated approval pathway allows drugs to be approved on surrogate markers of a disease,” Ross explained. “This suggests that when we’re allowing surrogate markers to form the basis of an approval, we’re not getting as many insights on the clinical outcome at the time of approval.”

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Drugs used to treat psychiatric conditions were also more likely to be associated with a post-market safety concern.

As for how this study could inform how the FDA evaluates drugs going forward, Ross points out that “you’re never going to have perfect evaluation,” but that, “some of the smaller risks can [still] be identified.”

The issue, though, for patients is more pressing. “In [a] post-market period, average time to detect a safety issue was between four and five years, many patients are using these drugs without a comprehensive understanding of their safety,” Ross said.