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.
6/20/15 JR
Cytochrome P450 2D6 (CYP2D6) is a liver enzyme responsible for the metabolism of approximately 30% of all drugs.
Milk thistle is often used to treat chemotherapy-associated liver toxicity.
Dr. Sharon Jacob from the University of Miami/Jackson Memorial Medical Center in Florida and colleagues 
Milk thistle is sometimes taken as a natural treatment for liver problems.
Here’s a follow-up to an earlier 
Researchers from Johns Hopkins University in Baltimore have 
Milk thistle is used as an alternative therapy for liver disease.
Researchers in the Hepatitis C Antiviral Long-Term Treatment Against Cirrhosis (HALT-C) Trial looked at the use and response to silymarin (milk thistle extract) among the patients in the study. 
The review