A smoker’s lung treatment sold by Germany’s Boehringer Ingelheim and U.S. drugmaker Pfizer was found to have improved the quality of life in patients after a nine-month period, study suggests.

Smoker’s lung or Chronic obstructive pulmonary disorder (COPD) is a disease marked by breakdown of lung function and chronic breathlessness, and kills about 2.75 million worldwide every year.

Pfizer and unlisted Boehringer said that the study of 554 patients showed that 23 percent more patients on their drug, Spiriva, experienced a 4-point improvement in the SGRQ score, a measure of health-related quality of life, than those on a placebo.

Results of the study were presented at the International Conference of the American Thoracic Society.

SGRQ measures distress due to respiratory symptoms, the effect on mobility and physical activity caused by breathlessness and the social impact on day-to-day life.

Sales of Spiriva more than doubled last year to 525 million euros ($664 million). Boehringer has said it expects the medication’s sales to attain blockbuster status, or $1 billion, this year.

Spiriva was launched last year in the United States and Japan and is expected to provide strong competition to Daxas, a treatment from fellow German firm Altana that has been filed for approvals in Europe.