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

Karl Marx described religion as the "opium of the people" because he viewed it as a form of ideological alienation that obscures the reality of human suffering under capitalism.12

In Marx’s analysis, religion functions as a tool that dulls the critical faculties of the working class. By projecting the need for liberation into a transcendental or heavenly sphere, religion encourages individuals to accept their wretched material conditions as part of a divine plan rather than recognizing them as the result of class struggle and exploitation.23

Marx considered religion to be a product of human consciousness—a reflection of a society where individuals have become alienated from their own labour and creative potential. Because he believed that existence determines consciousness, Marx argued that religion would not disappear through mere intellectual critique, but only through fundamental changes in the social and economic structures of society.13