Washington, Jan. 15 - Two men seeking to boost sexual performance and grow bigger muscles instead ended up with advanced prostate cancer after taking "herbal" supplements, U.S. doctors reported on Tuesday.
They said many supplements marketed as "safe" and "natural" could contain unknown and potentially dangerous ingredients, and noted that the U.S. Food and Drug Administration has little authority to regulate them.
"Physicians need to ask their patients not only about the prescription drugs they may be taking, but -- perhaps even more importantly -- about the over-the-counter drugs and supplements, which may have a profound impact on certain health conditions," Dr. Claus Roehrborn, chairman of urology at the University of Texas Southwestern medical school, said in a statement.
Roehrborn's team became concerned about what they call herbal/hormonal dietary supplements, or HHDSs, after two men developed aggressive and incurable prostate cancer within months of taking the same supplement.
They analyzed the product, which they did not name for legal reasons, and found it contained two hormones -- testosterone and estradiol. When they tested it on tumour cells in the lab, they found it fuelled the growth of prostate cancer cells more potently than testosterone alone, they reported in the journal Clinical Cancer Research.
"We filed an adverse event report with the FDA who issued a warning letter. The manufacturer responded by removing this HHDS product from the market," the researchers wrote.
"Individuals use HHDS for self-improvement, failure or distrust of conventional medicine, and because they believe that, these natural products are safe and drug-free," they wrote.
The researchers searched Web sites promoting such products and found they promised "'fountain of youth,' maintenance of a 'youthful' heart, relief of stress, and improvements in mood disturbances, stamina, energy, strength and virility."
The patients, a 67-year-old white man and a 51-year-old black man, have both survived but have extensive cancer that has spread throughout their bodies.
"Unlike prescription and over-the-counter drugs, the law does not require nutritional supplements to undergo pre-market approval for safety and efficacy," the researchers wrote.
"The Dietary Supplement Health and Education Act in 1994 (DSHEA) allows HHDS manufacturers to assume the sole responsibility for ensuring the effectiveness and safety of their products. Thus, the current Food Drug Administration regulatory system provides little oversight or assurance that HHDS will have predictable pharmacological effects or even that product labels provide accurate information to consumers."