Cantharidin in a collodion vehicle has been used by dermatologists as a treatment for molluscum contagiosum and warts since the 1950s.16,17 It satisfied all the safety requirements of the Food, Drug, and Cosmetic Act of 1938. However, in 1962, the FDA initiated an amendment to the Food, Drug, and Cosmetic Act, called the Drug Efficacy Study Implementation, which required manufacturers to submit efficacy data for their products.18 No efficacy data were submitted to the FDA, and cantharidin was removed from the market in 1962.19 However, the status of cantharidin may be changing in the near future. In 1997, President Clinton signed into law an amendment to the Food, Drug, and Cosmetic Act, adding section 503A, which provides that certain drug products may be compounded by a physician or a pharmacist on a customized basis for individual patients.20 Among other criteria, section 503A would permit the compounding of drug products that appear on a "Bulk Substances List," which is to be issued and maintained by the FDA. Although the list has not been finalized, cantharidin was 1 of 30 substances nominated for inclusion on the list. The FDA is on the verge of including cantharidin on its final "Bulk Substances List," along with other substances that are familiar to dermatologists, such as ferric subsulfate, iodoform, and thymol iodide. Diphenylcyclopropanone, squaric acid dibutyl ester, and others are still under consideration. In 1998, the FDA established an interim policy stating that, in general, it would not take regulatory action against drug products compounded with one of the substances nominated for inclusion on the list, as long as there did not appear to be a significant safety risk. Thus, a physician or pharmacist may administer drug products compounded with cantharidin, unless the FDA issues a notice that cantharidin appears to present a significant safety risk.21 Because of cantharidin's toxicity, the FDA has proposed that cantharidin should be limited to "topical use in the professional office setting only."