The drug Terbutaline (trade names Brethine, Bricanyl, or Brethaire) is a β2-adrenergic receptor agonist, used as a fast-acting bronchodilator and as a tocolytic to delay premature labour.
Terbutaline as a treatment for premature labour is an off-label use not approved by the FDA. Recent studies have suggested that terbutaline is a developmental neurotoxicant and may cause brain damage to the infant. (J Pharmacol Exp Ther. 2004 Feb;308(2):529-37. Epub 2003 Nov 10.)