Supplements may be a bad mix with some prescriptions

Millions of Americans pop nutritional supplements every day, but they may be unknowingly putting themselves at risk.

The overall supplements industry is worth $36.7 billion, and more than 53 percent of American adults use these products.

While pills like Echinacea and calcium have an image for being "natural," be wary, said CBS News medical contributor Dr. David Agus, director of the University of Southern California's Westside Cancer Center and the Center for Applied Molecular Medicine. In some cases, supplements can interfere with prescription drugs and treatments for serious health problems, including cancer, he said.

"Vitamins and supplements are an enormous industry in our country. We spend more on vitamins and supplements than on all of medical research in the United States. But many of these supplements change enzymes that metabolize drugs, and they can raise them up or raise them down," said Agus.

"When you're taking a drug - whether it be for blood clotting, chemotherapy, a thyroid disorder, or for something else - it can make the level higher or lower. The drug may not work or you may get undue side effects," he added.

Prescription drugs come with warnings, he explained, and pharmacists can red flag a new prescription medication if it mixes dangerously or badly with another prescription medicine a person is taking.

"But none of that is out there for these supplements. And so you just don't know most of the time," Agus warned.

Some of the interactions that can occur include:

• Mixing Echinacea -- which people often take for colds and flu, and which archaeologists believe Native Americans may have used for hundreds of years to treat infections and wounds, among other ailments -- with cancer drugs.

• Calcium, commonly taken by women for bone health, can interact with antibiotics or thyroid medication. And, Agus added, there's yet to be a positive study proving health benefits from calcium supplements.

• Ginkgo, touted to boost brain health, interacts with antidepressants and heart drugs.

• St. John's Wort, a supplement sometimes used for depression, mixes poorly with prescription antidepressants.

People often take supplements because a health care professional recommends it, but Agus cautioned, it's important to discuss their safety when mixing them with current prescriptions and when new prescriptions arise. Adding the information to your medical and pharmacy electronic health records is a good idea, too, including product names and dosages.