Another reason (as if one were needed) to doubt that "Soldier's Joy" meant "morphine" is that in the nineteenth century morphine was associated primarily with the relief of pain, not with getting high for the hell of it - an idea sensationalized by the press in the 1920s.

Soldiers and surgeons who saw that morphine was highly addictive would hardly have considered that to be a "joy." After a while, addicts need the drug just to feel normal.