This chapter presents the efficacy and adverse effects of the most widely used over-the-counter (OTC) drugs, vitamins/minerals, biologicals and herbal supplements by the older adult. It provides for the older adult and the healthcare provider relevant information to enable informed selection of OTC drug/dietary supplements. Although the use of OTC products in the older population is especially high, results of randomized clinical trials show that some products lack efficacy (multivitamins/minerals, calcium), interact with prescription drugs (OTC drugs and herbal remedies), should be avoided in the older adult (first generation antihistamines, nonsteroidal anti-inflammatory drugs) and are of dubious quality and quantity (biologicals, herbal remedies). Some OTC products exhibit efficacy in specific diseases and conditions but need to be used with caution (low dose/short term) or as with biologicals/herbal supplements, require the use of standardized validation preparations. Adverse effects of OTC products, whether alone or in combination with other OTC products and/or with prescription drugs, are discussed.