Formerly to impair the morals was a minor was a punishable offense.
The liver is one of the few human organs that regenerates, so having pieces removed usually does not impair function.
In other words, researchers were able to prove that THC should, technically, impair driving, but not that it does.
late 14c., earlier ampayre, apeyre (c.1300), from Old French empeirier (Modern French empirer), from Vulgar Latin *impeiorare "make worse," from assimilated form of in- "into, in" (see in- (2)) + Late Latin peiorare "make worse" (see pejorative). In reference to driving under the influence of alcohol, first recorded 1951 in Canadian English. Related: Impaired; impairing.