St. John's Wort for depression, garlic for a healthy heart, Chinese club moss for Alzheimer's... these herbal supplements are becoming increasingly popular in the United States.  Sales of these supplements have become a big business, with Americans spending more than $20 billion on alternative therapies last year.  But a battle rages over their efficacy and the U.S. government is investing more money into research on how well they work. 

Garlic is a key ingredient in many world cuisines -- and its advocates claim the aromatic bulb not only adds flavor to recipes, but can also help prevent heart disease.

Jim Duke of the Amazon Food Farmacy is a long-time advocate of using certain foods and herbal supplements as alternative therapies. "I recommend one clove of garlic a day for those who can take it, and your partner would have to take it as well for you to get along.  But garlic is a walking pharmaceutical firm, it's got at least 12 immune-boosting compounds, it's got at least 12 antiseptic compounds."

In light of those claimed properties, Americans are turning to herbal supplements in record numbers -- using them either as substitutes for medicines prescribed by their doctors, or often in addition to them.

At the first-ever Herb Day at the U.S. Botanic Gardens in Washington's Capitol Hill neighborhood, there were enthusiastic discussions about how herbal supplements can promote health.

But critics say such talk is unrealistic. Dr. Sid Wolfe of the American consumer watchdog group, Public Citizen, says people should be skeptical. "If they like their food that's seasoned properly, garlic is a good way to season food, but that's not the reason why it is sold. Claims such as cholesterol reduction, prevention of heart attack have been made and there is no evidence to support it."

The U.S. National Institutes of Health has tripled its budget for research into alternative therapies, including herbal supplements, since it launched its first studies in 1999. It now spends more than $300 million a year probing the efficacy of what is often called "complementary medicine".

One example:  at the University of North Carolina work is underway on whether Chinese club moss can be used to treat Alzheimer's, the brain-wasting disease.

Jim Duke is convinced that research will prove herbal supplements work.  "I am delighted to say that herbs are becoming evidence-based. We're really looking into such things. Well, you've heard of Cox-2 inhibitors, well you haven't heard much about natural Cox-2 inhibitors."

Cox-2 inhibitors are very expensive prescription drugs to treat arthritis, and some believe the spices turmeric and ginger can have similar effects. But Dr. Sid Wolfe of Public Citizen argues that scientific studies into herbal treatments are often flawed, making their conclusions unreliable.

"The government is beginning to test more and more of these against a placebo. The only way you can really test is to have half the people take a sugar pill and half the other and as they test these, one after another turns out to have zero benefit.  However, a number have some risk so there's an economic fraud, and no evidence of any benefit and some serious dangers."

But proponents of herbal supplements dispute this.   Dr. Robin DiPasquale is with Bastyr University, a Seattle, Washington-based institute that specializes in natural health sciences. She argues that scientific research will find that some herbal supplements do work if experiments are carried out effectively.

She is currently investigating claims about echinacea, a purple cone-flower often credited with boosting the human immune system and fighting the common cold. "The first level of research could be pharmalogical research where you could just test extracts of the plant to find components that you might want to be measuring.

The true research is clinical research when you actually apply it to patients.  And the problem with echinacea is there have been too many studies that haven't been designed appropriately, such as people not giving the proper dosing or dosing frequently enough or not using the correct part of the plant or the correct species of the plant.  So we're looking to do research that corrects those problems so the outcomes really reflect what's going on in clinical care."

While the debate over herbal therapies continues, experts say the first step before taking any medication or supplements is to consult a doctor. Not doing so can be dangerous. Certain supplements and medicines interact badly with one another, leading one-and-a-half million Americans being hospitalized each year for related problems.