Lead in ginkgo pills. Arsenic in herbals. Bugs in a baby's colic and teething syrup. Toxic metals and parasites are part of nature, and all of these have been found in "natural" products and dietary supplements in recent years.

Set aside the issue of whether vitamin and herbal supplements do any good.

Are they safe? Is what's on the label really what's in the bottle? Tests by researchers and private labs suggest the answer sometimes is no.

One quarter of supplements tested by an independent company over the last decade have had some sort of problem. Some contained contaminants. Others had contents that did not match label claims. Some had ingredients that exceeded safe limits. Some contained real drugs masquerading as natural supplements.

"We buy it just as the consumer buys it" from stores, said Dr. Tod Cooperman, president of ConsumerLab.com. The company tests pills for makers that want its seal of approval, and publishes ratings for subscribers, much as Consumer Reports does with household goods.

Other tests, reported in scientific journals, found prenatal vitamins lacking claimed amounts of iodine, and supplements short on ginseng and hoodia -- an African plant sparking the latest diet craze.

"There's at least 10 times more hoodia sold in this country than made in the world, so people are not getting hoodia," said Dr. Mehmet Oz, a heart surgeon and frequent Oprah Winfrey guest who occasionally has touted the stuff.

Industry groups say that quality problems are the exception rather than the rule.

"I believe that the problem is narrow, that the well-established and reputable brands deserve their reputations," said Michael McGuffin, president of the American Herbal Products Association.

Of course, prescription drugs have had problems, too. Dozens of deaths were linked last year to tainted heparin, a blood thinner produced in China, for example. However, pharmaceutical drugs must show evidence to the government of safety and effectiveness before they go on sale. Not so for dietary supplements.

Fifteen years ago, Congress passed a law that treats supplements like food and allows them to go straight to market without federal Food and Drug Administration approval. The FDA can act only after consumers get sick or a safety issue comes to light.

"We called it 'the body rule,'" said William Obermeyer, a chemist who left the FDA to found ConsumerLab.com with Cooperman. If a supplement was harmful, "we had to have so many adverse events before we could make a move on it. It was really like closing the barn door after all the animals left."

The law said the FDA could write quality control rules for products sold in the U.S. It took the FDA 13 years to adopt these, and they are just now taking effect. But the rules do not say what tests companies must do to prove what is in their products, and some tests can be fooled by subbing other ingredients. The rules also set no limits on toxins such as lead; nor do they change the fundamental way these products are sold to the public.

"It leaves the level of quality up to the manufacturer," Cooperman said.

In a written statement, FDA spokesperson Susan Cruzan said the new rules contain what is "needed to ensure quality," and that products that contain contaminants or whose labels do not honestly describe their contents, are considered adulterated and subject to further action by the agency. But she conceded that the agency is spread thin.

"In that FDA has limited resources to analyze the composition of food products, including dietary supplements, it focuses these resources first on public health emergencies and products that may have caused injury or illness," she wrote.

Millions of Americans take vitamin, herbal or other dietary supplements. Annual sales exceed US$23 billion, and more than 40,000 products are on the market. Tens of thousands of supplement-related health problems are handled by U.S. poison control centres each year, according to a report in the New England Journal of Medicine in 2002.

Until last year, supplement makers were not required to report problems to the FDA, and even now they must report only serious ones. The agency estimates that more than 50,000 safety problems a year are related to supplement use.

The Institute of Medicine, an independent science panel that advises the government, studied the situation in 2005.

"The committee is concerned about the quality of dietary supplements in the United States. Product reliability is low," says its report, which urged amending the 1994 law to tighten consumer protections.

Trade associations say the FDA's new rules do that.

"We are FDA-regulated products," though not in the same way as prescription or over-the-counter drugs, said Steven Mister, president of the Council for Responsible Nutrition.

The FDA can ask law enforcement to act against any company selling an adulterated product, said McGuffin of the herbal products association. "You can go to jail, you can have your company seized," he said.

"We represent companies that we consider the responsible centre of the industry," who are working to comply with the new rules, he said.

But his group only represents 250 of the 1,500 companies selling such products. And even though millions of people take supplements with no apparent ill effects, there have been many quality problems that a consumer might never realize because they don't always produce symptoms:

CONTAMINANTS

ConsumerLab.com found lead in at least one brand each of zinc, black cohosh and ginkgo products tested in recent years. Lead can accumulate and cause many health problems, and the testing company wants a national limit of 0.5 micrograms per day -- a level that in California requires a warning on the label.

A fungal toxin was found in four red yeast rice products in March 2008. And in 2007, federal officials warned about a liquid herbal supplement sold for colic and teething pain after finding cryptosporidium, a waterborne parasite that causes severe diarrhea.

Ayurvedics -- popular herbals used in traditional medicines from India -- often contain hazardous metals, studies in medical journals report. In 2004, researchers tested 70 ayurvedic remedies in the Boston area and found that one in five had potentially harmful levels of lead, mercury or arsenic. Tests in Houston, Chicago, San Francisco and New York City turned up similar results.

Metals naturally accumulate in certain herbs and come from the soil they are grown in. Many supplement ingredients come from Europe, India and China.

"We don't know how much of the ingredients are imported -- whether they're coming from across town or across the world," Mister of the trade association conceded.

But even manufacturers get duped, said Jana Hildreth of the Analytical Research Collective, a group of scientists advocating better supplement testing.

"Companies started going to China and demanding lower prices," and unscrupulous suppliers sometimes spiked products with cheap ingredients that can trick lab tests, she said. An example: a buckwheat derivative, rutin, in place of pricier ginkgo.

POTENCY PROBLEMS

In ConsumerLab.com testing last November, four out of seven supplements contained less ginkgo than claimed on their labels, and one failed to break apart properly to release its ingredients. Seven out of nine failed in tests in 2003, as did six out of 13 in 2005.

"It is now believed that ginkgo is among the most adulterated herbs," the company reports.

Tests by California scientists of two dozen ginseng supplements, reported in a nutrition journal in 2001, found that many differed from their labels. The concentrations of some ginseng compounds varied by up to 200-fold from product to product.

In ConsumerLab.com tests, six out of nine chondroitin supplements failed testing in April 2007. One had only 8 per cent of what it claimed to contain, and one "maximum strength" product had none.

Vitamins and minerals had problems, too. A "high potency" iron supplement contained less than half the amount claimed. Of 23 top-selling vitamin C pills, one provided less than half the amount promised; the suggested dosages of some others were beyond recommended safe levels. Of 10 vitamin A supplements, one provided twice its stated amount, raising concern about toxic side effects.

Last year, nearly 200 people were sickened by supplements containing up to 200 times the amount of selenium stated on the label. Symptoms included hair loss, discolored and painful fingernails, muscle cramps, joint pain, diarrhea and fatigue.

HIDDEN PRESCRIPTION DRUGS

The FDA has repeatedly warned about herbal pills found to contain versions of Viagra and similar drugs to help men get an erection. These can pose a heart hazard, especially when taken with certain medications.

In December, the FDA expanded warnings about dozens of brands of weight loss pills. Though the labels did not say so, some contained sibutramine, a controlled substance that poses heart risks; rimonabant, a drug not approved in the United States; a seizure medicine, and a diuretic.

Red yeast rice, a traditional Chinese medicine, has compounds that may block cholesterol in a way similar to statin drugs. Some red yeast rice products have been found to contain lovastatin, the active ingredient in the drug Mevacor. Problems can occur at high doses or with other medicines.

OTHER RISKS

Even "safe" supplements can be harmful. Beta-carotene takers still had increased rates of lung cancer six years after one study was stopped. These supplements "appear to increase rates of the disease, particularly among smokers," the National Cancer Institute warns.

In another study, men taking vitamin E were slightly more likely to get prostate cancer, and those taking selenium were a little more likely to develop diabetes. The results could have been due to chance, but federal officials were taking no chances and stopped the study last October.

Other studies suggest that high doses of vitamin C may help shield cancer cells from treatments designed to kill the cancer.

"Antioxidants are not the magic bullets that the supplement industry would like consumers to believe," said David Schardt, a nutrition expert with the consumer advocacy group, the Center for Science in the Public Interest. "They're not even necessarily benign."

Herbal sex pills containing the African tree bark extract yohimbe have landed men in hospitals with heart rhythm problems. This herb can cause high blood pressure, increased heart rate and other symptoms, the government warns.

The most serious side effects occurred with diet pills containing ephedra -- heart problems, seizures and even deaths. The FDA banned it in 2004. The battle started in 1997, when the agency wanted strong warnings on labels, and it became a test case of FDA authority that went all the way to the U.S. Supreme Court, where the FDA ultimately prevailed.

DRUG INTERACTIONS

Ginkgo, vitamin K, garlic, ginseng and other herbals can cause bleeding or clotting problems if taken with certain medications or before surgery. St. John's wort, promoted for depression, affects metabolism of more than half of all prescription drugs and can undermine birth control pills. Other supplements that can interfere with medicines include glucosamine, saw palmetto, soy and valerian.

OVERSTATED HEALTH CLAIMS

Makers can say a supplement addresses a nutrient deficiency, supports health, or reduces the risk of developing a problem, but then must say the product "is not intended to diagnose, treat, cure, or prevent any disease."

So consumers will see vague claims, such as "promotes healthy immune system function." The immune system has dozens of parts, and modifying one can be helpful or harmful, so "it's a quack concept," said Dr. Stephen Barrett, a retired physician who runs Quackwatch, a Web site on medical scams.

The Federal Trade Commission has stepped up actions against deceptive ads, said commission lawyer Rich Cleland.

"It is a little like playing Whack-A-Mole," because each time one problem is resolved, more seem to pop up, he said.

Last year, his agency reached a settlement against the makers of Airborne, a supplement aimed at people in crowded places such as airplanes, offices and schools. Company founders "made false claims that Airborne products are clinically proven to treat colds," and there is also no evidence the products can prevent colds, the FTC complaint says.

Airborne's makers agreed to add $6.5 million to the $23.5 million they had already agreed to pay to settle a related private class-action lawsuit, bringing the total settlement fund to $30 million.

Industry also has stepped up self-policing. The Council for Responsible Nutrition gave money to the Council of Better Business Bureaus so it could hire a lawyer to investigate some supplement sellers' sketchy claims.

"There were cancer cures and 'blast off 29 pounds in 39 days' -- really the Wild West of advertising. It was totally out of control," said the BBB's advertising division director, Andrea Levine.

The BBB council targets the worst claims in popular categories, such as diet, cold and flu, menopause, joint problems and sleep aids.

"We can't do them all," but want to send a broad signal about what kinds of claims are over the line for each type of product, she said.