If you've ever taken herbal products, seen a chiropractor or tried megavitamin therapy, you've ventured outside the boundaries of conventional medicine.

There's a term for those therapies -- "complementary and alternative medicine," or CAM -- and it describes the wide range of health systems, practices and products that fall outside the mainstream. The National Center for Complementary and Alternative Medicine (NCCAM) catalogues dozens of them -- from acupuncture to zinc supplementation.

The list of CAM therapies continually changes, as the ones proven safe and effective become well integrated into conventional medicine and new therapies are introduced.

There are also important distinctions between complementary and alternative medicine. Complementary medicine is something that is used in conjunction with conventional medicine, while alternative medicine is used in place of conventional treatment.

"You can have conventional cancer therapy along with, say, some music therapy or something that's soothing but relatively innocuous. It isn't going to affect your conventional treatment," explained Jackie Wootton, president of the Alternative Medicine Foundation in Potomac, Md.

"On the other hand," she added, "alternative medicine, such as coffee enemas, can be used as an alternative to conventional treatment."

In the United States, 36 percent of adults are using some form of complementary or alternative medicine, according to a 2004 study by NCCAM and the National Center for Health Statistics. The number rises to 62 percent when the definition of CAM includes megavitamin therapy and prayer specifically for health reasons.

According to the survey, prayer is the most commonly used CAM therapy. It is considered a type of "mind-body" therapy.

About one-fifth of people surveyed used natural products, such as Echinacea, ginseng, ginkgo biloba, garlic supplements and glucosamine.

Recognizing CAM's possible potential to prevent disease and promote wellness, some health care providers practice what is known as "integrative medicine," which combines conventional treatment with CAM therapies for which there is some evidence of safety and effectiveness.

But if, like many Americans, you see a conventional physician and use complementary or alternative medicine on the side, play it safe and tell your doctor what you are doing.

People shouldn't be afraid to broach the subject, Wootton urged. Physicians are much more accepting of CAM these days, and it's vital that they know what you are doing, she said, especially if you are ingesting something, such as herbal supplements.

Experts say one reason to share this information is the pittance of scientific evidence demonstrating the results of various therapeutic combinations.

"We know very little about the herb-drug interactions or the herb-herb interactions or vitamin-drug interactions," said Fredi Kronenberg, director of the Richard and Hinda Rosenthal Center for Complementary & Alternative Medicine at Columbia University in New York City.

You want your doctor to be in the loop because a particular supplement you are taking may interact either positively or negatively with a drug you are taking.

"It could interact negatively if you're taking a blood thinner and now you're taking a supplement that's a blood thinner, and now you get too much of a good thing," Kronenberg explained.

On the other hand, she added, "You could have a supplement that synergizes the effect of a drug -- that makes a drug work better -- and therefore you might need less of that drug."

Conventional doctors may not be CAM experts. But they are aware of some of the benefits and problems of CAM, Kronenberg pointed out. "And they're aware mostly that their patients are using these things, and they need to know about it if only because their patients are using them," she said.