Multivitamins - A Scoping Review of Clinical Trials Examining Their Efficacy and Safety

Multivitamins are widely used, but variation in formulations, populations, and outcomes complicates assessment of their benefits and risks. This scoping review mapped clinical trial reports evaluating broad-spectrum multivitamins in adults. MEDLINE/PubMed, Cochrane Library, and Scopus were searched from inception through 9 September 2026. Independent dual screening and standardized data extraction followed Joanna Briggs Institute methodology, with reporting guided by PRISMA-ScR. Eligible supplements were capsules or tablets providing, per daily serving, ≥50% of U.S. National Academy of Medicine life-stage-specific Recommended Dietary Allowances or Adequate Intakes for ≥14 vitamins and minerals, including ≥2 vitamins and ≥2 minerals, without exceeding any applicable Tolerable Upper Intake Level. The review included 157 articles: 103 primary intervention reports and 54 interim, secondary, or post hoc reports. The most consistent findings were improvements in circulating folate and vitamins B6 and B12. Effects on other vitamin biomarkers varied by context and baseline nutritional status, whereas mineral biomarkers showed few consistent improvements, except for iodine, iron and zinc, which were context dependent. Potential clinical benefits emerged in selected prenatal and cognitive contexts, although findings varied across outcomes, populations, and comparators. Findings for cardiovascular disease prevention were largely null. Multivitamins were generally well tolerated across the populations studied, including pregnant women, older adults, and surgical patients. However, formulation-specific adverse effects, such as mild gastrointestinal symptoms with some formulations containing iron or zinc, and potential drug-nutrient interactions, such as vitamin K with warfarin, warrant attention. These findings support a nutritional role for broad-spectrum multivitamins without implying universal disease prevention. Priorities for focused systematic reviews and trials include linking related reports, characterizing baseline nutritional status, assessing clinically meaningful outcomes, and consistently reporting formulations and harms. The review was preregistered on Open Science Framework (https://osf.io/t476d).