Terbutaline is a β2-adrenergic receptor agonist, used as a "reliever" inhaler in the management of asthma symptoms and as a tocolytic (anti-contraction medication) to delay preterm labor for up to 48 hours. This time can then be used to administer steroid injections to the mother which help fetal lung maturity and reduce complications of prematurity. It should not be used to prevent preterm labor or delay labor more than 48–72 hours. Terbutaline is currently on the World Anti-Doping Agency's list of prohibited drugs for Olympic athletes, except when administered by inhalation and a Therapeutic Use Exemption (TUE) has been obtained in advance. The tertiary butyl group in terbutaline makes it more selective for β2-receptors. Since there is no hydroxy group on the 4 position of the benzene ring - the molecule is less susceptible to metabolism by COMT enzyme.
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