United States health authorities issued a warning letter to leading global breast implant manufacturer Allergan for failing to properly carry out post-market safety studies.

The U.S. Food and Drug Administration found that Allergan did not meet its standards for recruiting and following up with participants in studies that included several styles of implants withdrawn from sale worldwide last year due to cancer risks.

Another company, Ideal Implant Incorporated, was rebuked for failing to properly track complaints by customers or take adequate corrective actions for problems identified during a site inspection.

“The FDA will continue to hold manufacturers accountable if they fail to fulfill their obligations,” Dr. Binita Ashar of the FDA’s Center for Devices and Radiological Health said in an agency statement announcing the warning letters.

In November 2018, the International Consortium of Investigative Journalists revealed that thousands of women around the world were suffering from serious illnesses after receiving breast implants, a finding that was part of its global Implant Files investigation.

In the months after the Implant Files’ publication, regulators around the world took action to better protect patients. Authorities in France, Canada, and the United States announced bans on Allergan Biocell implants, which were associated with increased risk of a rare form of cancer.

The moves prompted Allergan to announce a global recall of Biocell products last July. (Earlier this month, Allergan was acquired by global pharmaceutical giant AbbVie.)

The recalled implants are among the ones that Allergan was failing to properly study, the FDA found. The agency noted that the studies were crucial to identifying the risks for patients already implanted with Biocells.

“Post-approval studies are especially important to inform our understanding of the long-term potential risks associated with Allergan’s implants, including the models that have since been recalled from the market,” Ashar said in the FDA’s statement.

The agency touted the warning letters as a part of its “ongoing efforts” to better protect breast implant patients, also citing its Medical Device Safety Action Plan and the development of a National Breast Implant Registry to collect data on breast implant safety.

But Dr. Diana Zuckerman, the director of the National Center for Health Research, a health policy think tank, said the agency must also be willing to take tough measures against companies that fail to follow its rules.

Zuckerman noted that breast implant makers have a history of poor compliance with safety studies mandated by the FDA, which approved silicone breast implants for the U.S. market in 2006 despite scant data on their long-term safety.

Instead, the agency allowed manufacturers Allergan and Mentor to conduct long-term safety studies after their products were already on the market. Within three years, Allergan and Mentor lost touch with 40% and 80% of the patients, respectively, in key sections of these post-approval studies, torpedoing the FDA’s demand that they collect reliable long-term data.

Nonetheless, the agency permitted the implants to remain on the market.

Zuckerman was skeptical that the warning letters would have much effect unless the FDA showed it was willing to take products that violated its rules for safety studies off the market.

“It absolutely should be possible to take off the ones that aren’t studied properly,” Zuckerman said. “I guarantee if they did that the ones that are still on the market would finish their studies.”