Queen Victoria (May 24, 1819 – 22 January 22, 1901)
Sir John Russell Reynolds served a thirty-seven year tenure as Queen Victoria's personal physician. During his extensive services, Reynolds found cannabis useful for treating menstrual cramps, dysmenorrhea, migraine, neuralgia, epileptic convulsions, and senile insomnia. He wrote a scientific review of cannabis in 1890 that noted, "When pure and administered carefully, it is one of the most valuable medicines we possess." (J.R. Reynolds, "On the Therapeutical Uses and Toxic Effects of Cannabis Indica," Lancet 1 (1890): 637-38.)
We don't know whether or not Reynolds prescribed cannabis for his celebrated patient and paragon of morals, but it's likely he did.
Source: C. Conrad, Hemp for Health, 1997, Healing Arts Press (Rochester, VT)