Nearly 15 million Americans pay $300 million a year for pills, drops and lozenges made from the purple cornflower, echinacea, which looks something like the black-eyed susan. Western Indians used it a century ago for cough, hydrophobia and snakebite. Germans took it up, and it spread to the United States, first as a supposed antibiotic and in the 1960s as a cold remedy. Health food stores sell it as a “natural” but unregulated product. A recent study suggests it would serve more effectively, in flower form, as a table decoration.

Scientists at the University of Virginia, in a recent study in the New England Journal of Medicine, suggest that the herb doesn’t ward off colds. In the study, about 400 volunteers took either echinacea (pronounced eki-NAY-shia) or a sugar pill and had cold viruses dripped into their noses. Investigators watched them during five days in seclusion in hotel rooms. They found that both groups, those who took echinacea and those who took the sugar pill, fared exactly the same. They were equally likely to catch colds, and the symptoms were just as severe.

The head of the sponsoring government agency, Dr. Stephen E. Straus, director of the National Center for Complementary and Alternative Medicine, concluded that echinacea is not an effective cold remedy. He told The New York Times, “We’ve got to stop attributing any efficacy to echinacea.”

Still, health food stores so far notice little or no change in buying behavior. Their customers mostly either haven’t heard of the new study or else doubt its significance. Although the researchers used a dosage most commonly used by consumers, critics say it wasn’t enough. They cite other tests that they say showed positive results for the drug.

In any event, echinacea seems to be harmless for most people unless they are allergic to plants of the daisy family. And, although this recent test seemed to rule out any “placebo” effect, many authorities see beneficial health effects in “positive thinking,” including faith in a questionable remedy.

So, despite this new finding, taking echinacea may satisfy the classic medical dictum “do no harm.”

Yet this supplement, along with other botanical remedies, ought to be regulated by the U.S. Food and Drug Administration, like other medications. Only a powerful lobby and the popularity of “natural” remedies have shielded them from having to meet tests for safety and effectiveness.