Widely-used antidepressants could prevent infections which shorten the lives of many cystic fibrosis patients.
The lung disease is caused by a genetic mutation which creates the perfect environment for bacteria to thrive and cause permanent damage.
German and US scientists, writing in the journal Nature Medicine, say experiments on mice have revealed how this happens.
The most obvious symptom of the disease is the production of too much thick mucous inside the lung, which scientists had believed helped bacteria such as Pseudomonas aeruginosa to get established out of the reach of the body's immune system.
However, the work by the German and US teams suggests that a direct result of the genetic mutation is to lower the acidity within certain parts of the cell. This, in turn, interferes with the efficiency of two body chemicals whose job it is to control levels of a fat called ceramide.
Rising levels of ceramide cause increased inflammation and death of lung cells, which make it easier for bacteria to survive. Scientists believe that it may be possible to halt this chain reaction with the use of drugs.