The FDA has issued an advisory to consumers, urging them not to buy or use an array of products that, on labeling, contain hyaluronic acid but that contain “hidden” ingredients that are not included in the labeling. The products — including Curcuflex, DINA Acido Hialuronico, KUKA FLEX CBD, Umary, and others — are marketed and sold as joint pain relief treatments online at sites such as ebay.com and possibly in some retail stores, the agency said.