(MONEY Magazine) – Not that long ago, taking herbs and supplements other than a multivitamin was decidedly fringy. By 1999, supplements were a $14.7 billion industry, according to the Nutrition Business Journal, and mainstream corporations were marketing their own brands.

But shopping for a bottle of, say, ginkgo is different from shopping for vitamins. With herbs and supplements, you may not know what dose you're getting--or how it compares with what you need. What's more, dietary supplements, whether herbs or other compounds, don't have to undergo extensive testing for safety and effectiveness the way drugs do and can't legally claim to have curative effects. So if you pick up a supplement that "helps maintain healthy emotional balance" (Saint-John's-wort) or provides "optimal support for joint health" (glucosamine/chondroitin), and the language on the bottle seems vague, it is. The National Institutes of Health is sponsoring studies of Saint-John's-wort, ginkgo and glucosamine/chondroitin, but results are years away.

In the meantime, MONEY consulted leading experts about six of the most popular supplements. All our sources advise checking with your doctor. Some supplements interact with prescription drugs; others may cause allergic reactions.

When shopping for herbs, look for a brand that lists the "standardized extract" (the concentration of the active portion of the plant) in each dose, so you know what you're getting. Herbal dosages in this article were recommended by Varro Tyler, professor emeritus of pharmacognosy at Purdue University.

HERBS

Saint-John's-wort: Lab tests indicate that Hypericum perforatum, or Saint-John's-wort, is similar to prescription antidepressants like Prozac and Paxil. German studies show that it eases mild depression and anxiety. Before taking it, though, it is imperative that you see a health professional in order to rule out either severe depression or other diseases. Like Prozac, the herb needs a few weeks to take effect, says Dr. Steven B. Karch, a toxicologist-pathologist and author of the Consumer's Guide to Herbal Medicine.

Concerns: Saint-John's-wort can cause photosensitivity, so avoid sun exposure. Taking it with prescription antidepressants could cause an overdose. The herb dulls the effects of the HIV drug indinavir and the transplant drug cyclosporin.

Dosage: 300mg, three times a day

Standardized extract: 0.3% hypericin

Cost: About $25 a month

Saw palmetto: Regular use can relieve symptoms of enlarged prostate--a problem for more than half of men over the age of 50. You should see a physician first to rule out cancer. According to Dr. Karch, saw palmetto is most useful for those with mild symptoms who take it early.

Concerns: Independent testing by the research company ConsumerLab.com showed that only 17 out of 27 brands delivered the recommended dosage.

Dosage: 320mg a day

Standardized extract: 85% to 95% fatty oils and sterols

Cost: About $15 a month

Ginkgo biloba leaf extract: Chinese herbalists have used ginkgo for centuries. Advertising suggests it improves mental alertness and memory. Keep in mind that the research backing up this claim was done mainly on people who suffered from memory deficits and dementia.

Concerns: Ginkgo may interact dangerously with aspirin and prescription blood thinners like Coumadin. Be sure the product you choose to take does not contain ginkgo seeds, which are toxic. Among 30 brands that were tested, one-quarter flunked at least one of ConsumerLab.com's quality tests.

Dosage: 60mg to 120mg, twice a day

Standardized extract: 24% flavonoids, 6% terpene lactones

Cost: $15 to $30 a month

Black cohosh: Nearly a dozen human studies point to the effectiveness of this herb in treating menopause symptoms. Black cohosh appears to contain no estrogens, so taking it is not likely to prevent heart disease or osteoporosis the way hormone replacement therapy does; however, for those who cannot take estrogen, black cohosh may be a useful alternative.

Concerns: Traditionally, the herb has been used to induce labor.

Dosage: 40mg a day

Standardized extract: 40mg crude herb

Cost: $5 to $18 a month

NONHERBAL SUPPLEMENTS

Glucosamine/chondroitin: Buzz is growing about these natural alternatives to prescription anti-inflammatories for joint pain. Enthusiastic experts speculate that they may even rebuild worn-out cartilage. "There is very good evidence that glucosamine significantly reduces the pain of osteoarthritis of the knee," says Dr. William J. Arnold, rheumatologist and editor of the Arthritis Foundation's Guide to Alternative Therapies. But the compounds take at least two months to produce a noticeable improvement, if any.

Concerns: Chondroitin may increase chances of bleeding among those taking blood thinners. Diabetics should be aware that, in some animal studies, glucosamine increased blood-sugar levels. The allergic should know that glucosamine is extracted from crab, lobster and shrimp shells.

Dosage: 750mg of glucosamine twice a day; 600mg of chondroitin twice a day

Cost: $25 to $50 a month

SAM-e: This supplement--which is prescribed by doctors in Europe to combat depression, osteoarthritis and fibromyalgia--zoomed to top-seller status in this country about a year ago. According to research done in Europe, SAM-e helps the body make and regulate hormones, neurotransmitters and cell membranes; build cartilage; and produce glutathione, a compound that the liver uses to clear itself of poisons.

The most solid SAM-e research documents its effects on depression. But check with a doctor before taking it, warns Dr. Maurizio Fava, director of the depression clinical research program at Massachusetts General Hospital. Fava prescribes SAM-e to patients who don't respond to standard antidepressants.

Concerns: If you have bipolar disease or manic depression, SAM-e could trigger a manic phase.

Dosage: Dr. Fava gives his patients 1,200mg to 1,600mg a day for depression; arthritis sufferers may get by on 200mg.

Cost: $60 to $230 a month

--NATASHA RAFI