While green tea in and of itself may have beneficial anticancer properties, when taken with a widely used anticancer drug, Velcade, also called bortezomib, it may actually inhibit the drug’s effects on cancer patients.

Researchers from the University of Southern California Keck School of Medicine in Los Angeles found that some components in green tea may prevent bortezomib from killing cancerous tumor cells.

The researchers stressed that the negative effects of green tea only appeared in patients being treated with bortezomib and not other cancer-fighting agents, but they said that "patients currently undergoing bortezomib therapy should refrain from drinking green tea products, especially highly concentrated forms of teas." Bortezomib attacks cancer by inducing tumor cell death. But the researchers found that some polyphenols and other green tea components actually prevented bortezomib from doing its job.

"The green tea polyphenols appeared to have the potential to completely negate the therapeutic uses of bortezomib," they said. "While green tea components appear to interfere with the ability of bortezomib to combat cancerous tumor growth, other cancer-fighting agents may not be similarly affected.

However, the news is not all bad. "Green tea is a proven beneficial herb that has been shown to improve the anticancer effects of other drugs," according to the study.