horn" (probably actually narwhale
tusk) was considered a remedy for many things in early European forms of folk medicine
A whole unicorn horn could heal any wound, cure any illness, make unsafe water pure. It was said, howe'er, that the horn lost its power over time, being detached from its magical host. it could last many years and even several generations, but eventually a new one was required.
And oddly enough, the spent and power-drained horns were usually ground up into powder... which was then taken as a fairly strong aphrodisiac. (The magic-full ones of course were MUCH more potent, but too valuable to waste in such a manner.)