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By Natalie Grover

Feb 29 (Reuters) - The U.S. Food and Drug Administration has asked German drugmaker Bayer AG to conduct further studies on its controversial birth control device, Essure, and recommended that the product label contains the most restrictive type of warning.

Essure, acquired by Bayer in 2013, has been the target of thousands of complaints and calls for its withdrawal since it was approved for sale in the United States in 2002.

The device, promoted as an alternative to tubal ligation, consists of two small nickel-titanium coils inserted into the fallopian tubes. Scar tissue that forms around the device is meant to prevent pregnancy.

Complaints have included reports of the device breaking, moving and causing life-altering side-effects ranging from chronic pain and bleeding to autoimmune disorders such as psoriasis and lupus.

The FDA has instructed Bayer to conduct a clinical study to determine heightened risks for some women and has issued draft guidance with labeling recommendations, including a "black box" label warning of serious risks.

The agency also issued a checklist for doctors to use when discussing the risks of implanted permanent birth control devices. (http://1.usa.gov/1XV3fFu)

Bayer estimates there are about 750,000 women using Essure worldwide, about 70 percent of them in the United States.

Personal injury lawsuits filed against Bayer have also claimed the implant had caused allergic reactions, severe pelvic pain and required surgeries to stabilize or remove the device.

More than 5,000 adverse events involving Essure have been reported, according to the FDA's website, although the role of the device is not always clear.

Women using the device are more than 10 times likely to require post-procedure surgery than those who undergo laparoscopic sterilization, according to a study published in the British Medical Journal in October.

The FDA also ordered Bayer to conduct a trial designed to provide data on the "real world" risks of using the device.

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In September, the FDA called a meeting of its advisory panel to weigh the benefits and risks of Essure.

On Monday, the agency said that while it believed Essure was an appropriate option for most women seeking a permanent form of birth control, some may be at risk of serious complications.

Bayer said it would work with the FDA, while reiterating the positive benefit-risk profile of Essure.

Many members of a 27,000-member Facebook group "Essure Problems" expressed disappointment at the FDA's announcement. The group, as well as consumer watchdog Public Citizen, has been pushing for a ban on the device.

(Reporting by Natalie Grover in Bengaluru; Editing by Savio D'Souza and Ted Kerr)