Citricidal is a brand-name supplement, based on a component found in grapefruit pulp and seeds. Known as an antimicrobial compound, the seeds and pulp of grapefruit have a variety of properties, including use as a fungicide, antiviral and broad-spectrum, bacteria-fighting capabilities. Generally known for its low toxicity levels and safety, grapefruit seed extract is commonly purchased from drug stores and health food stores for its therapeutic antioxidant effects, to preserve cosmetics and foods, and in animal feed to help prevent parasites and mold, as well as a disinfectant for fish and poultry. However, as with anything, too much of a good thing can be bad for you. Some drug interactions are cautioned.