One of the enantiomers has therapeutic activity and the other may be has less of that, or the other enantiomer has not therapeutic action, however has toxicity.

• 通常外消旋体药的对映体中仅有一个对映体具有治疗活性,而另一个对映体可能很少具有这种治疗活性,或者根本就没有治疗作用,甚至还有毒性。