A medicinal white oil composition is prepared from an isomerized base oil. The isomerized base oil is filtered through a filter bed containing an acid activated clay having a surface area of at least 100 m.sup.2/g, for the base oil to be in compliant with at least one of European Pharmacopeia 3.sup.rd Edition, US Pharmacopeia 23.sup.rd edition (USP), FDA 21 CFR 172.878 and FDA 21 CFR 178.3620(a) for direct food contact, and FDA 21 CFR 178.3570 (USDA H-1). The medicinal white oil in one embodiment has a UV absorbance at 260 to 350 nm of less than 0.1.