Well, King Gustav III believed coffee was poisonous so he conducted an experiment with two prisoners; making one drink 3 pots of tea a day and the other 3 pots of coffee a day.
He put two doctors in charge of monitoring the results, convinced that the coffee drinker would deteriorate quickly and die first.
Both doctors died before either of the prisoners.
Then Gustav was assassinated.
Finally, the tea drinker was the first of the prisoners to die - at the age of 83.