The FDA has drawn attention to serious potential complications from the permanent birth control device Essure, and has called on its manufacturer, Bayer, to study its risks.

Essure is a small coil that is inserted into a woman’s fallopian tubes, creating scar tissue that eventually blocks sperm from reaching eggs. The device has been on the market for 14 years, but now, the FDA is concerned about reports of complications like “persistent pain, perforation of the uterus or fallopian tubes from device migration, abnormal bleeding and allergy or hypersensitivity reactions,” the agency wrote in a press release.

Essure will now be accompanied by a “black box” warning on its product label and a new patient checklist for doctors to review. Bayer will be permitted to keep the device on the market for now—a decision that has drawn criticism from some—but will be required to study the device’s efficacy and complications in a real-world environment.

In an emailed statement, Bayer’s senior vice president and head of medical affairs Americas wrote, “Patient safety and appropriate use of Essure are our greatest priorities. A woman’s decision to choose a birth control method is a very important and personal one, and Bayer is committed to providing physicians with resources, tools and information to help them counsel women about Essure.”