Users and prescribers of Hoffman-LaRoche's acne drug Accutane (isotretinoin) and similar generic versions will now have to enroll in a national registry to guard against birth defects and other side effects, the FDA announced Friday. The drug's manufacturers developed the long-awaited registry more than a year after an FDA advisory panel recommended the agency should track women who could become pregnant while taking the drug. Isotretinoin can cause brain and heart damage in the fetuses of women using the treatment, even in small amounts, the FDA said. "This is as strong as the FDA can get," FDA commissioner Lester Crawford said this morning on CBS' The Early Show. "If a pharmacist, a wholesale drug company, or a physician does not wish to participate in this program, then they will not have access to the drug." Women of childbearing age will have to undertake some additional steps before using the drug. They must use two forms of birth control, get two negative pregnancy tests before their initial Accutane prescription, and show proof of another negative pregnancy test before each monthly refill. Generic manufacturers participating in the program include Genpharm, maker of Amnesteem which is distributed by Mylan/Bertek; Ranbaxy Pharmaceuticals, maker of Sotret; and Barr Laboratories, maker of Claravis. An estimated 100,000 prescriptions are written for isotretinoin each month.