Multivitamins, diet pills and energy boosters may not be the harmless substances you think they are.

In the first study of its kind, published Wednesday in the New England Journal of Medicine, researchers estimated that 23,000 people end up in the emergency room each year suffering from heart palpitations, chest pain, choking or other problems after ingesting dietary supplements. Most of those patients were young adults, children or the elderly.

While that number is a small fraction – just 5 percent – of the number of ER visits involving pharmaceuticals, the issue is a cause for concern because the market for herbal and complementary nutritional products remains largely unregulated. Surveys have shown that about half of U.S. adults used at least one dietary supplement in the past month and that there were more than 55,000 products on the market as of 2012. Out-of-pocket expenditures on these products is about a third of what people spend on prescription drugs.

In recent years, U.S. health officials have ramped up efforts to warn consumers about the potential dangers of these substances after several highly publicized cases of deaths of otherwise healthy individuals who took supplements. Last year, two people – Logan Stiner, an 18-year-old high school senior in Ohio, and 24-year-old James Wade Sweatt of Georgia, who was newly married and a recent college graduate – died of overdoses from powdered caffeine.

The study – conducted by a team from the Centers for Disease Control and Prevention and the Food and Drug Administration – tracked ER admissions at 63 hospitals throughout the United States from 2004 to 2013. Of the 23,000 visits, 2,000 resulted in hospitalizations.

Some of these products can affect the heart; some can cause swallowing problems; and all should be stored away from young children.