Heroin
Initially, heroin was invented during an attempt to produce a drug similar to morphine but less potent and less addictive. However, quite the opposite happened. Heroin turned out to be around two times more potent than morphine itself. It was then prescribed to treat coughs and other ailments, such as back pain and insomnia. From 1898 through 1910, these cough syrups were marketed as a non-addictive morphine substitute and quickly became the cause of one of the highest addiction rates among its users.
#18 The idea is that of sympathetic (imitative) magic : mices have good teeth, so they are good for ailing teeth... the same kind of "reasoning" is always used nowadays in... homeopathy !
#19 Some trepanated prehistoric patients have survived long enough for the bone to grow again around the opening !
#1 Maybe one was supposed to have masturbated with a handful of cornflakes. That certainly would have made it a lot less fun. (Cream on your cornflakes, anyone?)