Pure silybin was found to be unstable whilst silybin in silymarin was stable in buffers from pH 1.0 to 7.8. The metabolism of silybin was more severe when in its pure form as compared to silybin in silymarin, as tested in a range of biological fluids including plasma, intestinal fluid and liver homogenates. It would appear that components in silymarin have a stabilization effect on its main component silybin.