Nasty tasting stuff, camphorated tincture of opium.
Probably not much used now. To slow down diarrhea.
O.Henry mentions it is description of a pharmacy.

"The Blue Light scorns the labour-saving arts of modern pharmacy. It macerates its opium and percolates its own laudanum and paregoric. "

Webster's 1913 Dictionary

Definition: \Par`e*gor"ic\, a. [L. paregoricus, Gr. ?, from ?
addressing, encouraging, soothing; ? beside + ? an assembly:
cf. F. par['e]gorique. See {Allegory}.]
Mitigating; assuaging or soothing pain; as, paregoric elixir.


\Par`e*gor"ic\, n. (Med.)
A medicine that mitigates pain; an anodyne; specifically,
camphorated tincture of opium; -- called also {paregoric
elexir}.