I can't speak for soldiers "throughout history," but chances are that the physical and mental stresses of combat have long pushed men-at-arms to use of mind-altering substances.

That said, the US Civil War (1861-1865) produced a time of unprecedented morphine addiction in the American South. Morphine had been used throughout the nineteenth century to ameliorate a variety of ailments, and was even more frequently used upon advent of the hypodermic needle around 1860. Once the Union emerged victorious, the Confederacy had suffered numbers of casualties and in a sense lost an entire way of life. Addiction sprung from medical practice, as wounded soldiers continued their doses well past recovery, and postbellum depression, as men (and women) consumed the relatively respectable opiates over alcohol in an increasingly "dry" nation.

For example, one New York opium dealer noticed a surge in orders from the south after 1865. He remarked, "Since the close of the war, men once wealthy, but impoverished by the rebellion, have taken to eating and drinking opium to drown their sorrows."

Source: Courtwright, "The Hidden Epidemic: Opiate Addiction and COcaine Use in the SOuth, 1860-1920," The Journal of Southern History, Feb 1983.