Raloxifene is a selective estrogen receptor modulator (SERM) that is used to reduce the risk of invasive breast cancer in postmenopausal women with osteoporosis.
Researchers at Washington State University and the University of North Carolina at Greensboro evaluated the inhibitory effects of individual milk thistle constituents on the intestinal glucuronidation (detoxification) of raloxifene.
First, the details.
- The inhibitory effects of individual milk thistle constituents on the intestinal metabolism of raloxifene were studied in the lab.
- UDP-glucuronosyltransferase 1-1 (also known as UGT-1A) is an enzyme in human intestines, which along with UGT1A8, and UGT1A10 are critical to metabolizing and removing raloxifene from the body.
And, the results.
- Milk thistle components silybin A and silybin B were potent inhibitors of raloxifene metabolism.
The bottom line?
The authors concluded: “Silibinin and silymarin [the major active constituents] were predicted to increase raloxifene systemic exposure by about 5-fold, indicating a high risk of interaction. Safety of raloxifene is discussed here.
It’s understandable that these women seek CAM, including herbals, to supplement raloxifene treatment.
It needs to be studied in humans, but for now, the risk of taking milk thistle would seem to outweigh any potential benefits. Check with your healthcare professional.