Which medications stop labor from progressing?

None: Despite the fact that many obstetricians use medications like terbutaline, magnesium sulfate, and Nifedipine to prevent early labor from progressing, many studies show that they are not very effective....And, for active labor, there are no known medications, at this time, to stop progression.

Labor: Although not fda approved, terbutaline is often used. Also, ethyl alcohol (the kind you drink) has been used to slow the progression of labor.