Generational cohort membership shapes consumer values, media habits, health orientations, and purchase behavior in ways that remain underexplored in the Indian functional beverage literature. This study investigates generational differences in health drink consumption behavior among Gen X (born 1965–1980), Millennials (born 1981–1996), and Gen Z (born 1997–2012) consumers in Karnataka, India, using an extended Theory of Planned Behavior (TPB) framework. Beyond the core TPB constructs—attitude, subjective norms, and perceived behavioral control—we incorporate four additional constructs: social media influence, brand trust, health consciousness, and price sensitivity. Data were gathered from 520 respondents across urban Bengaluru and semi-urban Karnataka through stratified random sampling, with generational cohort serving as the primary grouping variable. Multi-group structural equation modeling (MG-SEM) was employed to test the equivalence and differential strength of TPB pathways across the three cohorts, following measurement invariance testing. Findings reveal that Gen Z consumers are most strongly influenced by social media influence (β = 0.51) and health consciousness (β = 0.44), while Millennials exhibit the strongest brand trust–intention relationship (β = 0.48). Health consciousness mediates the attitude–intention pathway across all three cohorts, with the indirect effect strongest for Gen Z (indirect β = 0.24, 95% CI [0.14, 0.35]). Gen X consumers demonstrate the highest price sensitivity effect on perceived behavioral control (β = 0.39). Attitude emerges as the strongest predictor of behavioral intention across all three cohorts, though its magnitude varies. The integrated model explains 61% of variance in consumption behavior. To our knowledge, this is the first study to employ a three-cohort MG-SEM comparison of extended TPB pathways in the Indian health drink context. Managerial implications for cohort-specific marketing strategy and public health communication are discussed.