Terpin, used as the hydrate (terpin·H2O), is an expectorant, used to loosen mucus in patients with bronchitis and related conditions.

It was used in the United States in the late nineteenth century, but was removed from marketed medications in the 1990s after the Food and Drug Administration (FDA) found a lack of evidence of safety and effectiveness.

Adverse reactions include depression of the respiration, sedation, coordination disorders, constipation, and urinary retention.

The high alcohol content (42 percent) may increase depression of the central nervous system, codeine metabolism, as well as abuse potential.

He reported that it acted upon the mucous membranes and also the nervous system in a manner similar to the oil of turpentine.