WASHINGTON (AP) – With nearly one-fifth of Americans taking dietary supplements, the Institute of Medicine has called for tougher regulations to make sure the products are safe and do what they claim.

The institute expressed concern about the quality of dietary supplements, saying ‘‘there is little product reliability.’’

This makes it difficult for health professionals to guide patients in use of supplements, the report said. The panel urged that Congress take steps to require improved quality control of supplements and to provide incentives to study the efficacy of the products.

In a 327-page report, the institute also urged that complimentary and alternative medical procedures, such as herbal remedies and acupuncture, be required to meet the same standards of effectiveness as conventional medical treatments.

Dr. Stephen E. Straus, director of the government’s National Center for Complimentary and Alternative Medicine, said requiring the same research standards ‘‘will further the scientific investigation of this new field, increase its legitimacy as a research area and ultimately improve public health.’’

Unlike drugs, which must be proven safe before they can be sold, the Dietary Supplement Health and Education Act allows sale of supplements unless the Food and Drug Administration can prove them harmful. The law also does not require manufacturers to report adverse reactions, as drug companies must.

The Institute of Medicine report said 18.9 percent of Americans reported in 2004 that they had taken a dietary supplement in the past year. The industry was responsible for $18.7 billion in sales in 2002.

A study by researchers at Harvard Medical School, found that about 35 percent of Americans have used some form of alternative medicine.

The biggest change was an increase in use of herbal supplements over the five years, the study said. The practice of yoga also increased.

The Harvard report, published in the journal, Alternative Therapies in Health and Medicine , said use of therapies such as acupuncture, biofeedback, energy healing and hypnosis remained essentially unchanged between 1997 and 2002, while the use of homeopathy, high-dose vitamins, chiropractic and massage therapy declined slightly.