A new study has uncovered widespread evidence of contamination and mislabeling of herbal supplements sold in the U.S. and Canada with experts now saying that use of these products is not recommended.

The New York Times is reporting on the study, conducted by scientists at the Biodiversity Institute of Ontario at the University of Guelph and published in the journal BMC Medicine, which used DNA barcoding to uncover a variety of serious problems with herbal supplements currently on the market.

Researchers selected 44 bottles of popular supplements sold by 12 different companies whose names were not disclosed in the study. One-third of those tested contained no trace of the plant advertised on the bottle.  Many others contained ingredients not specified on the label, such as powdered rice, soybean, and weeds.

"Among their findings were bottles of echinacea supplements, used by millions of Americans to prevent and treat colds, that contained ground up bitter weed, Parthenium hysterophorus, an invasive plant found in India and Australia that has been linked to rashes, nausea and flatulence," the Times reports.

One bottle of St. John's wort contained only Alexandrian senna which comes from an Egyptian shrub that is used as a laxative.

"Gingko biloba supplements, promoted as memory enhancers, were mixed with fillers and black walnut, a potentially deadly hazard for people with nut allergies," the article continues.

This is not the first time that studies have found large percentages of popular herbal products to contain ingredients other than what the label says, with some of those ingredients being potentially dangerous. But this study is one of the largest ever conducted and is backed by DNA testing which makes its findings particular credible.

“This suggests that the problems are widespread and that quality control for many companies, whether through ignorance, incompetence or dishonesty, is unacceptable,” said David Schardt, a senior nutritionist at the Center for Science in the Public Interest, an advocacy group. “Given these results, it’s hard to recommend any herbal supplements to consumers.”

There are an estimated 29,000 products currently being sold on the herbal supplement market which is a thriving $5 billion business in the U.S.

The problem is that this particular market is difficult to monitor.

"Under a 1994 federal law, they can be sold and marketed with little regulatory oversight, and they are pulled from shelves generally only after complaints of serious injury," the Times reports.

Dr. David A. Baker, a professor of obstetrics, gynecology and reproductive medicine, told the Times that he tested 36 black cohosh supplements from online and chain stores and found that a quarter of them contained nothing more than an ornamental plant from China.

Calling the state of supplement regulation “the Wild West,” he lamented the fact that so many people are unaware of how paltry are the safeguards in this industry.

“If you had a child who was sick and 3 out of 10 penicillin pills were fake, everybody would be up in arms,” Dr. Baker said. “But it’s O.K. to buy a supplement where 3 out of 10 pills are fake. I don’t understand it. Why does this industry get away with that?”

Many people use supplements as a way to avoid conventional medicine and "Big Pharma" and don't realize that they're accomplishing nothing more than substituting one set of problems for another.