Hot drops is a colloquial name for a product called No. 6 Rheumatic Drops that was popular for treating a number of illnesses, including dental pain, dyspepsia and rheumatism around 1850. But where it found non-medical use was as a flavouring agent in soda beverages due to it’s spicy, bitter character. It’s addition to rootbeer seem to give that popular soda some adult bite.