The FDA issued a warning today against using thickener when feeding premature infants. The agency has discovered that SimplyThick gel may cause serious damage to these babies’ intestines, NPR reports. Since opening an investigation on May 13, regulators have found 15 cases of such issues—including two deaths. In all cases, the prematurely born babies had difficulty swallowing, so SimplyThick was added to their formula or breast milk. SimplyThick says it’s investigating the issue as well.