One third of people with asthma may not actually have the condition either because it has got better, or they were wrongly diagnosed in the first place, a new study suggests.

Researchers selected more than 700 adults at random who had been diagnosed with asthma in the last five years and checked them again.

They found 33 per cent of people did not have the condition, and nine in 10 of those were able to stop their medication completely. Most had minor conditions like allergies or heartburn, and 28 per cent had nothing wrong with them at all.

"It's impossible to say how many of these patients were originally misdiagnosed with asthma, and how many have asthma that is no longer active," said lead author of the study Prof Shawn Aaron, senior scientist and respirologist at The Ottawa Hospital and the University of Ottawa, Canada.

"What we do know is that they were all able to stop taking medication that they didn't need - medication that is expensive and can have side-effects."