**Background:** During the COVID-19 pandemic, dietary supplements (DS) and herbal foods (HF) were widely promoted on social media and conventional media as preventive or therapeutic agents, despite insufficient scientific evidence. This study aimed to evaluate DS/HF consumption habits and associated beliefs among Turkish adults during the pandemic.
**Methods:** This cross-sectional online survey was conducted via SurveyMonkey between June and December 2021. Using convenience sampling, 2160 participants were recruited, of whom 1767 were eligible (aged 18–65, social media users, able to understand Turkish). Exclusion criteria were regular supplement use before the pandemic and chronic disease requiring dietary supplementation. The 44-item questionnaire assessed sociodemographics, COVID-19 infection and vaccination status, DS/HF use for prevention and treatment, and beliefs about effectiveness. Content validity index was 0.971 (average) and 0.863 (universal agreement); Cronbach's alpha was 0.971. Statistical analysis used chi-squared, Fisher exact, Student t, and Mann–Whitney U tests as appropriate, with significance at P < .05.
**Key Results:** The sample was 76.9% female, mean age 29.07 ± 11.50 years, mean BMI 24.60 ± 5.11 kg/m². Most had at least a high school diploma (90.8%), 17.8% were health workers, and 50.0% were vaccinated against COVID-19. Overall, 35.3% used DS/HF for prevention (45.8% of infected vs. 32.2% of non-infected, P < .001), and 61.7% of infected participants used DS/HF for treatment. For prevention, the most used DS were vitamin C (25.3% infected vs. 15.5% non-infected, P < .001), vitamin D (21% vs. 14.7%, P = .00), and multivitamin-multimineral (17.5% vs. 11.2%, P < .001). The most used HF for prevention were citrus (28.9% vs. 19%, P < .001), lemon juice (26.3% vs. 19%, P = .00), and ginger (20.5% vs. 13%, P < .001). For treatment, the most used DS/HF were vitamin C (35.7%), vitamin D (28.9%), multivitamin-multimineral (25.1%), citrus (43.3%), lemon juice (38.5%), and honey (31.9%). Physicians were the main source of information (40.9% for prevention, 41.1% for treatment), but news outlets (18.9%) and friends/relatives (16.5%) were also common for prevention. Supplements were mainly acquired from pharmacies (51.2% for prevention, 50.2% for treatment). The products most believed to be protective were citrus (74.2%), vitamin C (73.4%), garlic (73.2%), onion (68.0%), and vitamin D (67.9%). A majority believed DS/HF could substitute for medicine (62.8% infected, 58.0% non-infected) and were more reliable than medicine (68.4% infected, 64.2% non-infected). Only 20.3% of infected and 17.0% of non-infected believed DS/HF could replace vaccines.
**Clinical Implications:** This study reveals widespread use of and belief in DS/HF for COVID-19 despite insufficient evidence, with over 60% of infected participants using them for treatment and a majority considering them reliable substitutes for conventional medicine. Healthcare providers should proactively discuss supplement use with patients and address misconceptions. Public health campaigns should emphasize evidence-based COVID-19 prevention and treatment, particularly given that many participants relied on non-expert sources (news, friends/relatives) for information. The high level of belief in unproven remedies underscores the need for regulatory oversight of DS/HF marketing claims during public health emergencies.