Intentional non-adherence to medical recommendations (iNAR) and the use of traditional, complementary, and alternative medicine (TCAM) have important public health implications. Previous studies suggest that these behaviors may be linked to irrational beliefs, that is, a set of beliefs that do not adhere to the standards of normative logic, lack an evidence base, and persist even when confronted with disconfirming evidence, over and above other structural or psychological factors. The present study represents a large-scale preregistered examination of the cross-cultural robustness of the association between irrational beliefs and questionable health behaviors across diverse sociocultural contexts. Data were collected from 15,218 participants (69% women; Mage = 33.58, SD = 13.86) across 33 countries. We assessed lifetime prevalence of iNAR-12 using a 12-item self-report instrument (Purić et al., 2023), while lifetime use of TCAM practices was assessed using a 22-item self-report instrument (Purić et al., 2025). We also assessed magical health beliefs (Lindeman et al., 2000), extra-sensory perception beliefs (Branković, 2019), and belief in conspiracy theories (Knežević et al., 2024; Oliver & Wood, 2014). We used hierarchical linear modeling to test the associations between irrational beliefs and questionable health behaviors. To account for the fact that data were collected in different countries, the random intercept of the data collection country was included in all models (i.e. the country was treated as a random factor). Irrational beliefs (introduced as separate predictors) showed remarkably consistent associations with TCAM use (standardized multilevel estimate between .28 and .39 across irrational belief variables). At the same time, associations with iNAR were also consistent but smaller (standardized multilevel estimates between .11 and .16). These associations remained stable after controlling for national healthcare quality assessed via the Health Pillar of the Legatum Prosperity Index. Going even further, the effects also persisted after partialling out a broad set of country-level indicators, including economic development, inequality, institutional stability, educational outcomes, and cultural values indices (GDP per capita, GINI index, Fragile States Index, PISA scores, Tightness–Looseness Index, Hofstede’s Cultural Dimensions Index, and the Traditional/Secular–Rational Values Index). Together, the findings indicate that questionable health behaviors are systematically associated with irrational beliefs and that this association generalizes across sociocultural contexts. To improve adherence to recommendations and discourage reliance on potentially ineffective or harmful practices, effective public health interventions should thus incorporate targeting of irrational beliefs instead of only providing behavioral recommendations.

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Questionable Health Behaviors (QHBs),irrational beliefs,intentional Non-Adherence to Medical Recommendations (iNAR),cross-cultural research,Traditional Complementary and Alternative Medicine (TCAM)

• Psychology - Social Sciences