After having the implants removed in 2015, she said, her health has improved. Though she still has some bad days, Ms. Cook said, “It’s been like a 180.”
Silicone-filled breast implants were first marketed in the United States in the 1960s. Over the next few decades, reports of illness emerged. In 1992, silicone implants were banned, except for reconstruction after mastectomy or to replace a previous implant, and then only in clinical trials.
A flood of lawsuits followed.
Studies conducted afterward generally found no link to connective tissue disease, but a few did suggest a connection. In 1999, the Institute of Medicine, then part of the National Academy of Sciences, concluded that overall, there was no evidence that breast implants caused connective tissue disease, cancer, immune disorders or other ailments.
In 2006, silicone implants came back on the market. But manufacturers were required to follow large numbers of women for seven to 10 years, as a condition for F.D.A. approval. Deficiencies in the studies have now prompted the agency to send warning letters to two of the four companies approved to market breast implants in the United States.
One warning letter, sent to the manufacturer Sientra, of Santa Barbara, Calif. on Tuesday, said the company had not kept enough patients in its study of an implant approved in 2012, and warned that if the follow-up monitoring did not improve, the agency could withdraw approval of the implant, effectively taking it off the market. Sientra did not respond to a request for comment. Its stock price dropped a little more than four percent on the F.D.A. news.
Last September, the Securities and Exchange Commission accused its former chief executive, Hani Zeini, of concealing damaging information about the manufacturer of its implants before closing a $60 million stock offering in 2015. The Brazilian manufacturer had had a certificate of compliance required for selling in the European Union suspended. Sientra said its issue with the S.E.C. had been resolved.
The other letter went to Mentor Worldwide, owned by Johnson & Johnson and based in Irvine, Calif. The F.D.A. said the company had not enrolled enough patients in a study of its MemoryShape implant, approved in 2013, and also threatened to rescind approval for the product. Withdrawing approval for a medical device is time-consuming and rarely occurs.