The U.S. Food and Drug Administration approved Monday the first generic versions of the sleep aid Ambien — generic name zolpidem tartrate. It's a sedative-hypnotic drug indicated for the short-term treatment of insomnia.

In 2006, Ambien was the 13th best selling brand name drug, according to the online magazine Drug Topics. "This approval offers Americans more alternatives when choosing their prescription drugs," said Gary J. Buehler, director of the FDA's Office of Generic Drugs.

Zolpidem tartrate tablets in formulations of 5 milligrams and 10 milligrams are manufactured by a variety of generic drug companies in the United States. Thirteen manufacturers have received FDA approval to manufacture zolpidem tartrate tablets.

In March, the FDA requested that all manufacturers of sedative-hypnotic drug products — a class of drugs used to induce and/or maintain sleep — strengthen their product labeling to include stronger warnings about potential risks. Those risks include severe allergic reactions and complex sleep-related behaviors, which may include sleep-driving. Sleep driving is defined as driving while not fully awake after taking a sedative-hypnotic drug, with no memory of the event.

The sanofi-aventis (formerly Sanofi-Synthelabo Inc.) patent for zolpidem tartrate expired on April 21, the FDA said.