FRIDAY, Feb. 9 (HealthDay News) -- Patients in phase 1 cancer trials may be skewing the results if they are also taking vitamins, herbal preparations, minerals and other dietary supplements, researchers report.

More than one-third of patients in these trials report taking these alternative medications, according to a report in the Feb. 10 issue of the Journal of Clinical Oncology.

Phase 1 trials are designed to test the safety of an experimental drug and to determine if there are any harmful side effects. Since the biological activity of herbals and other natural supplements aren't always known, taking them could mask the effect of the drug under study, explained lead author Dr. Christopher Daugherty, an associate professor of medicine at the University of Chicago.

"If anything bad happens to a patient in a phase 1 trial, we attribute it to the experimental drug," Daugherty said. "But much of biologically active complementary and alternative medicines are agents that have not been well studied, and we don't know what their effects are in the body by themselves, let alone when they're combined with experimental drugs," he said.

"If we don't know what the effects of a alternative drug are, or if we don't know the patient is taking it, we can falsely assume that the experimental drug is unsafe or even safe," Daugherty said.

In the study, Daugherty's team interviewed 212 patients with advanced cancer enrolled in phase 1 clinical trials. Patients were interviewed about their use of biologically-based alternative medications.

The team found that 34 percent of patients were taking these supplements, similar to their usage in the general U.S. population. Among the patients, 41 said they were taking vitamins and minerals, such as vitamins A, C, D, E, and B12, selenium, magnesium, zinc, and copper. In addition, 40 patients said they took herbal preparations, including cat's claw, laetrile, St. John's wort, milk thistle, ginseng, and echinacea.

Although patients in phase 1 trials are not supposed to be taking other drugs, Daugherty believes that there are several reasons why the natural concoctions are often overlooked.

Sometimes, patients are reluctant to tell the doctor they are taking alternative medicines, either because they don't think it's important, or they don't want to be told to stop taking them, Daugherty said.

"Patients need to tell their doctor what medications they are taking, such as mega-doses of vitamins. These, by themselves, may do no harm, but if you combine it with other drugs that are metabolized in the liver, who knows what might happen," he said.

For example, St. John's wort can be toxic to the liver if it is taken along with certain chemotherapy drugs, Daugherty said. "On the other hand, some alternative medications may be protective against side effects. So, we may falsely assume that the experiment's drug is safe," he said.

Doctors too are often lax in asking their patients about alternative medicines. There may be several reasons for this, Daugherty said. On the one hand, doctors might not think to ask, and, on the other hand, they might not think the drug could cause a problem.

And, since it's often difficult to get cancer patients to take part in phase 1 trials, some researchers may be reluctant to turn any potential patient away. "In addition, most doctors don't know very much about alternative medicine," Daugherty said.

One expert believes that both patients and doctors need to be concerned about any medications participants are taking before they start a clinical trial.

"If people aren't being asked about alternative medications in this day and age -- that's a bad thing," said Dr. Tieraona Low Dog, the director of education at the program in integrative medicine at the University of Arizona.

Patients do need to be asked about alternative medications, because they can alter results, Low Dog said.

"If you are going to participate in a clinical trial, you have to be completely candid with the physicians and the researchers about what you have been using, and that's not just vitamins, minerals and herbs, that's also over-the-counter medications. Many of these things can affect the trial medication and your outcome," Low Dog said.

In addition, since alternative medicines are so common today, doctors need to specifically quiz their patients about them, Low Dog said. "If you don't ask, they won't tell."

More information

For more information on alternative medicine, visit the U.S. National Center for Complementary and Alternative Medicine.