For centuries Rock Candy has been recognized as having marked therapeutic and preservative qualities. In fact, in the West, sugar was used only as a medicine or preservative up to the middle of the 18th century when people "discovered" it made a sweet treat as well. The earliest known date that white sugar was refined was about 200 C.E. so it is probable that the further refining into what was later known as "Sugre Candie" was at about that time.
There are many references to what we now call Rock Candy in literature. There are several references to it in the poems of the Persian poet Jalal-ad-Din Rumi who lived in Turkey in the middle 1200's. One early English reference in 1584 seems to sum up the virtues of Rock Candy where it is quoted "White sugar is not so good for phlegume, as that which is called Sugar Candie." Shakespeare in Henry IV (1596) referred to its therapeutic value as a throat soother for long winded talkers.
Source: Dryden and Palmer