Treating or preventing symptoms caused by spasms or contractions of the muscles around the bronchioles (air tubes) associated with asthma, bronchitis, and emphysema. It may also be used for other conditions as determined by your doctor. Terbutaline is a bronchodilator. It works by dilating (opening) the bronchioles of the lungs by relaxing the muscles around them. This allows for easier airflow into and out of the lungs.