The hypodermic needle model (also known as the hypodermic-syringe model) is a model of communications also referred to as the "magic bullet" perspective, or the transmission-belt model. Essentially, this model holds that an intended message is directly received and wholly accepted by the receiver. The model is rooted in 1930s behaviorism and is considered by many to be obsolete today.
The hypodermic needle theory implied that mass media had a direct, immediate and powerful effect on their audiences. The mass media in the 1940s and 1950s were perceived as a powerful influence on behaviour change. Several factors contributed to this "strong effects" theory of communication, including: the fast rise and popularization of radio and television, the emergence of the persuasion industries, such as advertising and propaganda, the Payne Fund studies of the 1930s, which focused on the impact of motion pictures on children, and Hitler's monopolization of the mass media during WWII to unify the German public behind the Nazi party.
This view of propaganda took root after World War I and was championed by theorists such as Harold Lasswell in his pioneering work Propaganda Technique in the World War (1927). He argued that the people had been duped and degraded by propaganda during the war. Lasswell based his work on a stimulus-response model rooted in learning theory. Focusing on mass effects, this approach viewed human responses to the media as uniform and immediate. E. D. Martin expressed this approach thus: "Propaganda offers ready-made opinions for the unthinking herd" (cited in Choukas, 1965, p. 15). The "Magic Bullet" or "Hypodermic Needle Theory" of direct influence effects was not as widely accepted by scholars as many books on mass communication indicate. The magic bullet theory was not based on empirical findings from research but rather on assumptions of the time about human nature. People were assumed to be "uniformly controlled by their biologically based 'instincts' and that they react more or less uniformly to whatever 'stimuli' came along" (Lowery & DefFleur, 1995, p. 400).
The phrasing "hypodermic needle" is meant to give a mental image of the direct, strategic, and planned infusion of a message into an individual. But as research methodology became more highly developed, it became apparent that the media had selective influences on people.
The most famous incident often cited as an example for the hypodermic needle model was the 1938 broadcast of The War of the Worlds and the subsequent reaction of widespread panic among its American mass audience. However, this incident actually sparked the research movement, led by Paul Lazarsfeld and Herta Herzog, that would disprove the magic bullet or hypodermic needle theory, as Hadley Cantril managed to show that reactions to the broadcast were, in fact, diverse, and were largely determined by situational and attitudinal attributes of the listeners.