Washington ? The thousands of Americans who take the acne drug Accutane – and people who prescribe and dispense it – must enroll in a national registry, part of a major government program to tighten access to the medicine that causes birth defects.

The Food and Drug Administration enacted unprecedented curbs Friday in trying to keep Accutane and its generic competitors on the market while ensuring that women who use the risky pills don’t get pregnant. Critics see it as the drug’s last chance, after two decades of safety warnings and other restrictions failed to end Accutane-damaged pregnancies.

If a woman becomes pregnant while taking the acne drug, her baby can suffer severe brain and heart defects, mental retardation and other abnormalities.

Under the program, every patient – men and women – must enroll in the iPLEDGE computerized registry starting Dec. 31 to receive the drug.

Doctors must register, too, if they wish to continue prescribing the pills. The pharmacist must check the computer database before filling a prescription to ensure that patients followed all these rules.

Accutane is supposed to be used for severe acne only, but it is widely acknowledged to be prescribed for more minor cases. The FDA estimates that 100,000 prescriptions for Accutane and generics are filled each month.

The registry actually opens on Aug. 22. On that date, patients may enroll at http://www.ipledgeprogram.com or by phone at 1-866-495-0654.