Federal officials are warning health providers about weight loss balloon devices after five people died unexpectedly shortly after being treated with them.

The U.S. Food and Drug Administration (FDA) released a report that since 2016, five people died after using liquid-filled balloon weight loss system intended to treat obesity. In the procedures, patients are mildly sedated as a deflated balloon made of silicone is inserted through the throat and into the stomach, after which it’s filled with saline to take up space in the stomach. The balloon is designed to remain in place for several months. Four of the deaths occurred after patients used the Orbera Intragastric Balloon System, manufactured by Apollo Endo Surgery, and one took place after a patient used the ReShape Integrated Dual Balloon System, which is made by ReShape Medical Inc.

MORE: I Swallowed a Balloon For Weight Loss and Lost 40 Lbs.

In each case, the person who received the weight loss balloon died within a month or less of having the balloon placed. In three cases, the person died one to three days afterward.

“At this time, we do not know the root cause or incidence rate of patient death, nor have we been able to definitively attribute the deaths to the devices or the insertion procedures for these devices,” the FDA writes, adding that it is looking into two other deaths.

The alert from the FDA does not mean that the agency has definitively proven that the balloons caused the deaths, but that they are looking into it. The agency recommends that doctors closely monitor patients who are using these devices.

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