A new warning has come forth that “natural” dietary supplements, readily available on the Internet and displayed attractively in health food stores, supermarkets and convenience stores, are not always as safe as they sound.

Consumer Reports, in its May issue, concedes that most supplements are “fairly benign.” But it lists a “dirty dozen” as “too dangerous to be on the market,” on the basis of government warnings, adverse-event reports, and top experts. The magazine was able to purchase all of them easily in February in a few days of shopping online and in retail stores.

How can this be, in a nation whose government monitors hazards in the workplace, requires warnings on ladders telling people how high they can safely climb, and keeps close watch on all foods and drugs, whether prescription or over-the-counter? The answer is not only that the U.S. Food and Drug Administration’s supplement division is understaffed and underfunded, with a budget of $10 million to police a $19.3 billion-dollar-a-year industry. Even with an adequate staff and budget, its hands are largely tied by congressional restrictions.

Contrary to widespread belief, supplements don’t need government approval before they go on public sale. They require no testing for safety and effectiveness. Warning labels about potential side effects are not required.

Leading the Consumer Reports blacklist is aristolochic acid, sometimes marketed as birthwort, snakeroot, sangrel and wild ginger. It is a potent human carcinogen and has caused kidney failure and death. The FDA warned against it three years ago, and most European countries have banned it.

No. 2 is comfrey, also known as ass ear, blackwort, salsify and slippery root. It can cause liver damage and death. The FDA advised industry in 2001 to remove it from the market.

Third is andrestenedione, sometimes called andro or androstene. It increases cancer risk and decreases HDL cholesterol, the so-called “good” type. Athletic associations have banned it, and FDA warned companies last month stop making and marketing it.

Next comes chaparral, aka creosote bush, greasewood, jerillal and larreastat. It has damaged liver and sometimes caused death. The FDA issued a warning in December 1992.

The list goes on, including kava, an herbal tea widely warned against but still widely sold. Kava, like many others of the magazine’s dirty dozen, has been blamed for abnormal liver function or damage, occasionally irreversible, and sometimes death. Others on the list can cause heartbeat irregularity, breathing difficulty, dizziness, high blood pressure and stroke. Four of the supplements have escaped official warnings entirely but still are termed likely hazardous.

What to do about it? Consumer Reports says pending federal legislation may help, but the supplement retailers’ trade group is telling people through its Web site and leaflets that the proposed bills “would significantly undermine many of the freedoms that American consumers of dietary supplements like you hold dear.”

In the meantime, the magazine advises readers to steer clear of the dirty dozen, stay away from supplements promising weight control, limit intake of supplements, and tell your doctor what you are taking to avoid dangerous interactions with drugs. Finally, watch for possible side effects and report any to your doctor.

This is a timely warning and a call for long-overdue action.