(Reuters) - Health officials are banning the only asthma inhaler sold over the counter in the United States starting next year to prevent the use of products that harm the environment.

The Food and Drug Administration said on Thursday that chlorofluorocarbons (CFCs) in metered-dose asthma inhalers that contain the drug epinephrine cannot be used, following an international agreement that bans CFCs because they deplete the Earth's ozone layer.

Right now, the only such inhaler is marketed by Armstrong Pharmaceuticals, a unit of Amphastar. The company could not be immediately reached for comment.

The inhaler, called Primatene Mist, is used for temporary relief of occasional symptoms of mild asthma and is the only FDA-approved inhaler sold over the counter without a prescription, the FDA said.

The product uses CFCs to propel medicine out of the inhaler so patients can breathe it into their lungs. The FDA said some manufacturers now use a propellant called hydrofluoroalkane instead, which is less harmful to the environment.

The FDA first proposed phasing out the use of CFCs in asthma inhalers with epinephrine in 2006, and finalized the phase-out in November 2008.

Primatene Mist inhalers are already labeled to show they cannot be used after Dec. 31, 2011. After that, the FDA said, some consumers may have to pay more for prescription asthma inhalers.

About one million to two million patients use Primatene Mist, although it is difficult to get an estimate of how many people use over-the-counter drugs, the FDA said.

More than 235 million people worldwide suffer from asthma and it is the most common chronic disease among children, according to the World Health Organization.

Two other prescription asthma inhalers that use CFCs are to be phased out by the end of 2013. These are Boehringer Ingelheim's Combivent Inhalation Aerosol and Graceway Pharmaceuticals' Maxair Autohaler.

The United States has generally banned CFCs in consumer products such as hairspray since 1978, but their use has been permitted in medical products when the FDA deems it essential.