Why did Karl Marx describe religion as the opium of the people?

Karl Marx described religion as the "opium of the people" to characterize it as a form of ideological alienation that provides an illusory comfort to those suffering under the conditions of capitalist society.1

Influenced by the work of Ludwig Feuerbach, Marx viewed religion as a human projection—a distorted representation of reality created by individuals who have become alienated from their own creative labor and humanity. In this view, religion functions as a "generalized theory of the world" that offers a sense of solace or hope in a transcendental sphere, effectively masking the material causes of suffering and exploitation.123

By providing this illusory justification for the status quo, religion acts as a sedative that obscures the reality of class struggle and the alienation inherent in market production. Marx argued that because religion is a product of these specific social and economic conditions, it would not simply disappear through intellectual critique alone; rather, it would only cease to exist once society itself was transformed to resolve the underlying material contradictions that necessitate such illusions.13