Shares of DexCom were spiraling after the medical device company surprised Wall Street with a steep cut to guidance, and grim news about its performance in the second quarter. DexCom stock slumped 40% to $64.70 in trading Friday and was on track for its worst daily percentage decline on record, according to Dow Jones Market Data. The stock slid last fall on fears around anti-obesity drugs, or GLP-1s—the company designs and sells continuous glucose monitors for diabetics—but that doesn’t appear to be dragging shares lower Friday.