(Reuters) - The New York State Attorney General issued subpoenas in July to three firms that make energy drinks, including PepsiCo Inc, seeking information on the companies' marketing and advertising practices, a person familiar with the matter said on Tuesday. Besides Pepsi, maker of AMP, Attorney General Eric Schneiderman also sent subpoenas to Monster Beverage Corp and Living Essentials LLC, maker of the 5-Hour Energy drink, said the source, who declined to be identified, citing lack of authorization to speak to the media. A spokeswoman for Schneiderman declined to comment, as did PepsiCo. Living Essentials also declined to comment beyond...