Complementary Health Approach Use Among Adults Reporting a Clinician Diagnosis of Chronic Fatigue Syndrome in a US Online Quota Sample

Background/Objectives: We compared reported complementary health approach (CHA) use by self-reported clinician diagnosis of chronic fatigue syndrome (CFS), with favorability and expected helpfulness as additional exploratory outcomes. Methods: This secondary analysis included 3022 adults from a 2024 US nonprobability online quota sample. Diagnoses were not clinically verified, and formal ME/CFS criteria were not assessed. Logistic models adjusted for ten covariates, using Firth regression for sparse or unstable estimates. Revision-time Benjamini–Hochberg correction defined nine question-based families by outcome and approach grouping. Results: Among 167 respondents reporting CFS, adjusted odds of use were higher for physical (aOR 2.22, 95% CI 1.60–3.07), nutritional (2.25, 1.34–3.80), combined (1.89, 1.24–2.88), and systems approaches (1.99, 1.32–3.01); all q < 0.05. Nineteen individual CHAs and all seven conventional approaches met q < 0.05 for use. Any-CHA use was 98.2% versus 94.6% (aOR 2.46, 95% CI 0.97–8.91; q = 0.065). Adding the count of other self-reported clinician diagnoses attenuated category-use associations; their CIs included 1. Psychological-category favorability was lower using a mean >3.5 cutoff, but its FDR threshold status depended on midpoint handling. No expectancy association met q < 0.05. Conclusions: Respondents reporting CFS reported greater use of multiple approaches. Additional-diagnosis adjustment changed the estimates, but the count cannot distinguish morbidity from healthcare contact or diagnosis ascertainment. The findings do not establish CFS-specific treatment use, substitution, or effectiveness.