WASHINGTON – Three members of the U.S. Congress have signed letters sent to 14 companies that sell energy drinks. The letters ask such questions as why the companies market the energy drinks the way they do, what ingredients are in the drinks and what claims do they make in their marketing campaigns. One question deals with marketing energy products to children or teenagers while another asks if the company markets its product as a supplement or conventional food or beverage.

Senator Dick Durbin of Illinois, Senator Richard Blumenthal of Connecticut and House of Representatives member Ed Markey of Massachusetts, previously have sent letters to the Food and Drug Administration and the Federal Trade Commission about the safety of energy drinks. All three Congressmen signed letters dated Jan. 17 that were addressed to such companies as PepsiCo, Inc., Coca-Cola and Dr Pepper Snapple Group as well as companies that sell such drinks as Red Bull and Monster Energy.

“Energy drink companies need to be clear with consumers about what they think their product is, what it contains and what it can do,” Mr. Markey said. “The broad claims made by these products and their blurred classification in the marketplace make it difficult for consumers, particularly young consumers, from making informed decisions about their consumption.”

The F.D.A. is working on a draft guidance designed to clarify for industry the line between dietary supplements and conventional foods and beverages. The F.D.A. also is investigating adverse health reports, including deaths, involving Rockstar Energy, 5-Hour Energy and Monster Energy. The reports do not represent any conclusion by the F.D.A. about whether the products caused the adverse events.

“As new products and new patterns of energy drink use are emerging, we are working closely with the F.D.A. to strengthen our understanding of the potential health impact of these products,” Mr. Durbin said. “Energy drink companies can partner in our effort by being forthcoming about the ingredients in their products and the processes they use to determine those ingredients are safe.”

Rodney Sacks, chairman and chief executive officer of Corona, Calif.-based Monster Beverage Corp., spoke about the safety of energy drinks in a Dec. 11, 2012, investors’ meeting. He said energy drinks are as safe as coffee purchased at coffee houses, and recent comments questioning the safety of energy drinks are comparable to comments questioning the safety of soft drinks decades ago.