As shocking as it may be to some people, there are shady companies out there hawking supposed “dietary supplements” that actually contain harmful, illegal drugs. Since many consumers trust anything labeled “natural” or marketed as a non-drug, this practice has a potential for negative consequences.

The New York Times takes an in-depth look into the problem, which can involve substances as dangerous as carcinogens and amphetamines. Ingestion of some of these tainted supplements has resulted in kidney failure, heart problems, depression and addiction.

It’s illegal to market drugs as health supplements, and the practice has legal supplement suppliers like GNC worried about their business, which reached $28.1 billion last year. Customers might get too spooked over the idea black-market goods in the guise of legal supplements, to shop for dietary supplements containing only vitamins and minerals.

The most common tainted products include those sold touting weight loss, bodybuilding and sexual enhancement.

Warns the NYT:

Some of these products, according to the F.D.A., contain amphetamines, synthetic steroids, laxatives and compounds like the active drug in Viagra. Officials say such products can cause heart attacks and strokes, and can damage the kidneys and liver. A few people in the United States, they say, have died after taking them.

Before you go into a panic in the vitamin aisle, experts say the vast majority of supplements are just fine. The bottom, safe line: shop at large chains and go for brands with wide name recognition like Centrum, One A Day and Nature Made.

Or hey, eat right, go to the gym and eat oysters.

Ingredients of Shady Origins, Posing as Supplements [New York Times]

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