Background: Nutraceutical interventions have been investigated in thyroid dysfunction, but biological plausibility, antibody responses, and clinical efficacy are often interpreted as equivalent outcomes.
Objective: To critically examine their mechanisms and clinical effects of nutraceuticals for hypothyroidism, hyperthyroidism, Hashimoto’s thyroiditis, and Graves’’ disease.
Methods: A structured narrative review integrated human studies identified through directed searches of bibliographic records, accessible primary publications, regional literature, and gray sources. Selected primary studies and relevant evidence syntheses were prioritized. Outcomes were interpreted according to diagnosis, nutritional status, concurrent treatment, comparator, and clinical relevance.
Results: Selenium studies demonstrate a separation between immunological and clinical responses. Meta-analytic reductions in thyroid peroxidase antibodies coexist with substantial heterogeneity, while CATALYST trial found no improvement in quality of life or levothyroxine requirements. GRASS trial did not improve Graves’ remission, and selenium findings in orbitopathy varied between settings. Myo-inositol plus selenium, Aloe vera, Nigella sativa, and selected botanical preparations showed preliminary biochemical or symptomatic effects. Brazil nuts increased T3 and free T4 in selenium-deficient hemodialysis patients, representing indirect evidence for primary thyroid disease. L-carnitine primarily targets peripheral hormone action. Pharmacological iodine suppresses thyroid activity in selected Graves’ settings, whereas desiccated thyroid extract is hormonal treatment.
Conclusions: The evidence supports intervention-specific and outcome-specific interpretation. Nutrient repletion, immunomodulation, altered drug absorption, and symptom relief are distinct therapeutic effects. Most preparations lack replicated evidence for sustained recovery of endogenous thyroid function or durable remission. Future trials should test defined clinical phenotypes, standardized formulations, and patient-relevant outcomes.