There has been much historical research into the question of the rise and dissemination of opium in world history, particularly in early-modern India and China, where it enjoyed particularly widespread use.
The first, and certainly most important, reason that opium use was tolerated in this period is because it made European traders and imperial monarchs a profit. Colonialism in the 1700s and 1800s was predicated on extracting raw materials and selling back finished products in order to generate enormous amounts of revenue. In his monograph Forces of Habit: Drugs and the Making of the Modern World, for example, David T. Courtwright argues that although opium was looked upon by suspicion by many colonial governments, it inevitably entered enormous global markets. In addition to serving as a major commodity for sale on the international black market, opium provided a way for British colonists specifically to control the population in China and India, where people particularly enjoyed the product.
Opium held a place of significance in the Chinese mentality. During the Great Manchurian Plague of 1910–1911, for example, Chinese observers in the afflicted city of Harbin believed that those who had been killed by the plague had actually been killed by smoking inferior grades of opium. By this reasoning, the epidemic could be eliminated simply by importing in finer-quality opium and distributing it to the poorer population.
The British used these superstitions to their great advantage. Courtwright has stated that imperialists used opium to energize laboring populations. Drugs, especially narcotics like opium, can facilitate the backbreaking work that industrial-era production in factories and plantations demanded. Opium both motivated exhausted laborers to work harder and diminished the pain they felt as a result of their physical effort. Thus, both directly through its sale and indirectly as a result of the increased productivity it guaranteed, opium was a useful tool of colonial rule.
Though China and India were the most vivacious consumers of opium, colonialists also used the drug to great effect in Malay, Egypt, Jamaica, and Europe itself.