ROCHESTER, Minn. -- Sales of herbal dietary supplements have skyrocketed by 100 percent in the United States during the last 10 years, but most people dont consider evidence-based indications before using them, according to a University of Iowa study published in this months Mayo Clinic Proceedings.

Two-thirds of people who use herbs dont do so in accordance with scientific guidelines, according to the article. Meanwhile, sales of herbal supplements reached $18.8 billion in 2003, up 100 percent from $8.8 billion in 1994. Those sales are subject to minimal federal regulations.

Physicians are concerned, says Aditya Bardia, M.D., lead author of the study and a resident in the Department of Internal Medicine at Mayo Clinic, because herbal supplements can have adverse side effects and interact negatively with therapeutic drugs. Physicians should ask patients about herb use during every clinical visit and hospital admission to better inform patients about potential benefits and harm, agree the studys authors.

Physicians, pharmacists and other health professionals should proactively educate consumers and advocate for public health policies that would disseminate evidence-based information regarding the appropriate use of herbs, Dr. Bardia says.

To generate their findings, physicians culled information from a 2002 National Health Interview Survey taken among U.S. adults. The final study population, 609 adults, took a single herb and said they were taking it to treat a specific health condition.

The study found that only one-third of this population took the herbal preparation for a known scientific indication. Dr. Bardia cautions that further study is warranted as the efficacy of herb use evolves and says much more needs to be learned about the clinical indications for individual herbs.