This article reports that for non-asthmatics it may not make a difference.
Elite-level athletes with documented proof that they have asthma are allowed to take certain inhaled corticosteroids, which prevent inflammation of airways and can hold asthma symptoms at bay.
And they are allowed to take other inhaled drugs, beta-2 agonists, which relax the smooth muscle cells of airways, relieving symptoms. A few of the beta-2 agonists can increase muscle and decrease body fat if they are injected or taken orally.
But when they are inhaled, in doses used to control asthma, beta-2 agonists do not improve performance, asthma and doping experts say. And neither do corticosteroids.
“A lot of people believe they are performance enhancers,” Dr. Gary I. Wadler said about inhaled asthma drugs. But, added Wadler, who is chairman of the World Anti-Doping Agency’s prohibited list and methods subcommittee, “there is no evidence for that at all.”
http://www.nytimes.com/2008/07/22/sports/olympics/22asthma.html?scp=1&sq=asthma%20doping&st=cse