IQVIA Holdings Inc. shares dropped 4.5% in extremely heavy Wednesday afternoon trade before being halted on Wednesday after the Food and Drug Administration raised serious concerns with the company’s data, which tracks the amount of pharmaceuticals sold in the U.S., and in particular data related to controlled substances like prescription fentanyl. While doing an analysis, the regulator said it discovered a more than 20% discrepancy between the amount of prescription fentanyl actually sold in the U.S. over the last five years and IQVIA’s database. After conducting an investigation and speaking with the company, the FDA said that past prescription fentanyl data were overestimated because of an error in the company’s methods, likely related to using the wrong conversion factors to figure out how much fentanyl is in a given unit. The overestimation for fentanyl distributed in the U.S. marketplace was specific to estimated volume in kilograms, the regulator said, information the FDA uses “only narrowly,” in quota recommendations made to the Drug Enforcement Administration. But the error also extends to several other controlled substances, such as oxymorphone and hydrocodone, raising “serious concerns about systemic issues with IQVIA’s data and quality control procedures,” the FDA said. IQVIA is now conducting a review to ensure estimates are accurate, but the FDA is also asking it to hire a third-party auditor and give more insight into how its data is generated. IQVIA also recently announced a secondary public offering of 10 million shares at a price of $101.85 per share, along with plans to buy back 2.5 million shares, an offering that’s expected to close on Friday. IQVIA shares have declined 4.2% over the last three months, compared with a 0.3% decline in the S&P 500 and a 1.8% drop in the Dow Jones Industrial Average .