A novel approach to treating asthma — which causes the worsening of symptoms to improve them later — can lead to long-term, improved respiratory function, suggests new research.

Asthma is traditionally treated with drugs called agonists, which open inflamed and constricted airways to improve breathing.

But a new, counterintuitive method in which antagonists called beta blockers are given to worsen breathing, is showing that the reverse may be more effective.

Beta blockers are drugs that block adrenaline in the body, allowing the heart to beat more slowly and lowering blood pressure. They allow blood vessels to relax, increasing blood flow.

They have traditionally not been prescribed to treat asthma because they intensify asthma symptoms.

While beta agonists' effectiveness worsens over time, when patients in a clinical trial were given beta blockers, their respiratory function improved after an average 28 days. The researchers believe that the drugs allow the smooth muscles that line the airways to dilate, allowing more air to pass through them.

The study, which followed a mouse study that had similar results, involved treating patients with mild asthma with nadolol, a beta blocker. While their breathing worsened initially, all participants tolerated the drug and 80 per cent reported improvement, according to the study.

The finding does not remove the need for inhalers that can treat an acute attack.

"Even if I am correct about beta blockers ultimately being used in the treatment of asthma, there probably always will be a need for the inhaler-type agonist drugs to handle acute asthma attacks," said  Richard Bond, associate professor of pharmacology at the University of Houston.

"I do believe, though, that beta blockers hold promise in a maintenance or preventative regimen that could reduce the number or severity of attacks and improve a patient's quality of life."

The study is published in the March issue of the American Journal of Respiratory Cell and Molecular Biology.