This study was designed to determine the safety of a medical food, flavocoxid, a proprietary blend of free-B ring flavonoids and flavans from the root of Scutellaria baicalensis (Chinese skullcap) and the bark of Acacia catechu in the dietary management of knee osteoarthritis. The 12-week, randomized, double-blind, placebo-controlled trial in an academic medical center enrolled 59 patients with moderate osteoarthritis of at least one knee who were recruited who were classified as having "below average" to "a moderately above average cardiovascular risk" with a Framingham-based scoring tool. Subjects were randomized to flavocoxid 250 mg twice a day versus identical placebo. Safety measures, including recording of adverse events, incidence of serious adverse events, and results of routine laboratory values, were compared between the two groups. There were no major differences in the baseline demographic characteristics of the placebo and flavocoxid groups. With one exception no significant differences were found between the two groups with respect to adverse events by body system, blood pressure, or laboratory values. There was a significantly higher incidence of upper respiratory adverse events in the placebo group (35.4% vs. 5.8%, P = .0003). There were no intra- or inter-group differences in any of the laboratory parameters from study baseline to completion. Thus, flavocoxid is safe when used in a population with "below average" to "moderately above average cardiovascular risk" compared to placebo.