DNA doesn’t lie.

And when scientists from the University of Guelph scoured the DNA in a number of herbal products, they found that many times the labels on the merchandise didn’t accurately reflect what was in the container.

Some products contained fillers like wheat or rice that were not listed on the label. Some were contaminated with other plant species that could have caused toxicity or triggered allergic reactions. And still others contained no trace of the substance the bottle purported to contain.

“It says ginkgo biloba . . . and we didn’t find any ginkgo DNA at all in the bottle,” said Steve Newmaster, an integrative biology professor at the university who was the first author on the paper.

In fact, about a third of the 44 products Newmaster and his co-authors tested were instances of what he called product substitution — alfalfa sold as ginkgo, for example. He said those two substances in powder form would be indistinguishable without testing.

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People buying herbal products need to know they may not be getting what they are paying for — and they may be ingesting something they aren’t expecting, said Newmaster, who is also the botanical director of the Biodiversity Institute of Ontario, which is the home of the Canadian Centre for DNA Barcoding.

“Because you spend a lot of money to buy a health product, you care about your health, and then you’re not getting what you think you’re getting.”

The study is being published Friday in the journal BMC Medicine.

Though Newmaster used the term product substitution, he noted a switch might not be deliberate, at least on the part of the manufacturers or distributors.

He and his colleagues shared their findings with some of the companies whose products they tested, and he said they expressed surprise and dismay.

Heather Boon, interim dean of pharmacy at the University of Toronto, said companies do have quality control measures in place and raw materials should come with a paper trail. But to some degree everyone is dependent on the honesty of the players in the system.

“So as a company, you do your best, I would argue — I hope — to ensure you trust the suppliers you’re getting (materials from), but ultimately they can’t control it in most cases from the ground to the bottle,” said Boon, who studies complementary medicines and natural health products.

She said Canada has relatively new regulations meant to improve the quality of natural health products sold in this country and she believes the situation is better than it was in the past. But she admitted the findings of Newmaster’s study are a worry.

“I’m concerned as a consumer. I’m concerned as a scientist. We know that lots of people are taking these products.”

The findings come as no surprise to David Bailey, a pharmacist and professor emeritus at Western University in London, Ont., who has studied natural health products and the way they can interact with prescription drugs.

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“It is a common problem and it really is a ‘buyer beware’ phenomenon,” said Bailey, who last year published a study detailing the interaction of grapefruit juice with many medications.

Bailey said the problems identified in Newmaster’s study — product substitution, contamination, use of fillers and undisclosed ingredients — have all been seen before, though he said the technology used here to find the results was an interesting development.

“This is an ongoing problem,” he said of the quality of the products.

Newmaster said the science is “CSI”-like. He and his colleagues extract DNA from the pills, capsules or powder in a supplement bottle, and compare what they find to a library of DNA barcodes for various plants. The same technology has been used to determine the diet of endangered animal species by mining their feces for DNA.

In this study, the team tested 44 herbal products sold by 12 different companies. The study does not reveal brand names.

Nearly 60 per cent of the products contained DNA from at least one plant species that wasn’t listed on the product label. Some St. John’s wort, for instance, contained senna, which can be toxic if taken regularly, Newmaster said, adding senna can cause chronic diarrhea and can damage the colon and the liver.

More than 20 per cent of the products contained fillers such as rice, soybeans and wheat. People trying to stick to a gluten-free diet would not know to avoid them because these filler ingredients were not listed on labels.

Newmaster noted the numbers here are small — on average, fewer than four products per company were tested. He suggested a larger study should be done.

But two of the companies came through with a perfect record — all their products were what they claimed to be. Conversely, all the products of two other companies either contained contaminants or undisclosed fillers or were not the product they were supposed to be.

Herbal products are big business, part of the enormous natural health products market which is estimated to generate billions of dollars of sales a year in North America alone.

A 2010 Ipsos Reid poll done for Health Canada found that 73 per cent of Canadians admit to using natural health products of some sort, even though half of the people polled were skeptical about the health claims made by manufacturers and 42 per cent were dubious about the quality of these products.

Still, people routinely self-prescribe natural health products, said Bailey, who noted that the fact that some contents are not disclosed on the label means people who have been warned to avoid certain drug-herbal interactions can’t be sure they are going to be able to do so.