The U.S. Food and Drug Administration said it was reexamining San Diego-based Acadia Pharmaceuticals’ drug to treat hallucinations and delusions caused by Parkinson’s disease. The news was first reported by CNN on April 25.

Acadia’s stock closed at $15.20, a 21.6 percent drop from the day’s opening.

Several weeks ago the FDA began taking another look at Acadia’s Nuplazid, which the agency approved, according to CNN’s April 25 article. The FDA didn’t specifically say why it’s reexamining the drug, only that the agency identifies “potential signals of serious risk/new safety information” by looking at adverse event data. The FDA is not recommending patients stop taking the drug while the evaluation continues.

It's not clear how long the reexamination may take.

Earlier this month, CNN highlighted a November publication from the Institute for Safe Medication Practices, which noted reports of more than 200 deaths of patients who had been using the drug through March 2017.

The adverse event reports, which are reviewed by the FDA, do not mean that a suspected medication has been proven to cause the harm and are typically not the result of official investigations. But the FDA uses the reports to gauge potential issues with a drug.

A reviewing panel approved the drug by a 12-2 vote, according to CNN, but some members of the committee who voted in favor of it expressed concern about the limited testing the drug had undergone at the time.

Nuplazid earned a “breakthrough” designation from the FDA, expediting its path to market.

Acadia did not immediately return a question to comment.