The New York attorney general has subpoenaed three large makers of so-called energy drinks as part of an investigation into whether the companies are misleading consumers about how much caffeine the drinks contain and the health risks they could pose.

The attorney general, Eric T. Schneiderman, is also looking at whether the companies — Monster Beverage, PepsiCo and Living Essentials — violated federal law in promoting the drinks as dietary supplements rather than as foods, which are regulated more strictly.

State authorities are also concerned about whether all of the ingredients that go into the beverages are properly disclosed, according to an official briefed on the investigation who spoke on the condition of anonymity.

The state investigators are also examining whether some additives, like black tea extract and guarana, may contain additional caffeine that is not reflected when the drinks are labeled.