People in the U.S. spent $33.9 billion last year on alternative health goods and services, ranging from antioxidant supplements to yoga, according to a new study released today by the National Institutes of Health (NIH).

About 38 percent of adults are using some sort of alternative treatment (known as “complementary and alternative medicine” or CAM), and what they’re buying makes up about 11 percent of total U.S. out-of-pocket health care spending, the report states.

“With so many Americans using and spending money on CAM therapies, it is extremely important to know whether the products and practices they use are safe and effective,” Josephine Briggs, director of NIH’s National Center for Complementary and Alternative Medicine, said in a prepared statement.

Spending on natural products ($14.8 billion), such as omega oils or St. Johns Wart, of which the effectiveness remains unproven by the U.S. Food and Drug Administration (FDA), was about a third of what people spent on prescription drugs annually; and total visits to alternative treatment practitioners, such as chiropractors or acupuncturists, were equivalent to about a quarter of the out-of-pocket money spent on physician visits.

“This underscores the importance of conducting rigorous research and providing evidence-based information on CAM,” Briggs said, “so that health care providers and the public can make well-informed decisions.”

With about $4.1 billion going to yoga, tai chi and qigong classes (and $200 million to other relaxation techniques) annually, are Americans any more equanimous? A study by the American Psychological Association in 2007 (the same year the CAM data was collected) found that about half of Americans reported an increase in stress over the past five years and more than two thirds of Americans reported physical and/or psychological symptoms of stress.

If alternative medicines still seem like a gamble, keep in mind that spending on these treatments was just a touch less than the $34 billion people lost in nontribal-owned U.S. casinos last year.

Image courtesy of iStockphoto/evgenyb