The maker of PC-SPES recalled the product due to the fact it may be tainted with a prescription drug. The government has warned patients to stop using it now.

On Feb. 8 the Food and Drug Administration (FDA) warned people to stop taking PC-SPES after sample tests showed it contained the prescription drug warfarin, a blood thinner often sold under the brand name Coumadin.

"I think it's very important for patients who are taking PC-SPES to talk to their doctors," said David Rosenthal, MD, of Harvard University, chair of the American Cancer Society (ACS) advisory group on complimentary and alternative medicine.

PC-SPES is a blend of eight herbs, and is made by BotanicLab and sold without a prescription. It has shown such promise in treating advanced prostate cancer that it is now being compared in tests with hormonal therapies, the standard treatment for the disease.

A Los Angeles Times article reported that at least 10,000 men in the US used PC-SPES last year. As an over-the-counter supplement, it is not overseen by the FDA.

The maker has recalled the product, stating that unused capsules should be returned to BotanicLab, which can be reached at 1-800-458-5854.

Patients with advanced prostate cancer who took the herbal treatment PC-SPES saw a sharp rise in levels of prostate-specific antigen (PSA) in their blood when they stopped taking it, said a study in the journal Cancer (Vol. 94, No. 3: 686-689).

Prostate cancer often depends on male hormones to grow. Treatments for advanced disease work by keeping those hormones in check.

But some patients have tumors that no longer respond to hormone treatments, including the four men studied at Dana-Farber Cancer Institute in Boston, whose cases were reported in the journal article.

These men were taking PC-SPES, but stopped because it was no longer working for them. Within one month of stopping, their blood PSA levels — which tend to show whether the cancer is growing — increased up to 880% higher than during therapy.

The rise was rapid and much higher than expected, but doctors aren't sure what to make of it.

"Four cases are a small number and this study represents an attempt to simply share this with doctors, so that they would be aware of this possibility," said William Oh, MD, lead author and a doctor at Dana-Farber Cancer Institute.

These patients didn't have an increase in symptoms such as pain. An increase in PSA level often is a sign of growth of cancer, said Oh. But, it's possible that PSA changes do not always correlate with changes in the cancer cells themselves, he said.

Although Oh assumes this may be the case here, "We cannot be sure, and I would recommend that patients discuss with their doctors how to react to rapid rises in PSA," he said.

Rosenthal said patients should always keep their doctors informed about any alternative medicines or vitamins they're taking. He said some of the biggest problems in medicine today are interactions between drugs, herbs, and anti-oxidants.

"Some of these interactions are very harmful, very toxic, and potentially fatal," he said.

Many health care workers, such as Rosenthal, are calling for standards for herbal and other over-the-counter remedies so that patients will know what they are taking when they swallow a pill.

"This is not just about PC-SPES," he said. "There are so many vitamins and antioxidants on the market that vary from batch to batch, and who knows what's in them. This is a big problem and needs to be fully addressed."