WASHINGTON — Federal regulators yesterday unveiled a high-tech system to restrict distribution of Accutane, an acne drug taken by thousands of Americans.

The drug has been particularly effective against severe acne, but has long been known to cause birth defects and is now being studied for a possible connection to teenage suicides.

The Food and Drug Administration enacted unprecedented curbs in the effort 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 prevent Accutane-damaged pregnancies.

Patients, doctors, pharmacists, wholesalers and manufacturers all will be required to enroll and participate in an Internet-based tracking system, called iPledge, which will go into effect Dec. 31.

Women of childbearing age will be required to submit the results of monthly pregnancy tests, and all patients will have to acknowledge that they understand the potential for psychiatric side effects, which also will be emphasized in stronger warning language.

The registry actually opens Aug. 22, giving users time to learn how it works before the provisions become mandatory at year's end. On that date, patients may enroll at www.ipledgeprogram.com or by phone at 866-495-0654.

Although welcomed by some experts, the FDA actions are unlikely to satisfy critics who say the agency has neglected its duty as a drug-safety watchdog. Accutane has been on the market since 1982, and these critics say the new measures will not keep doctors from prescribing it to patients who may not need such strong medicine.

Accutane was one of five drugs named last fall in congressional testimony by FDA whistle-blower Dr. David Graham as deserving a critical re-examination of their risks and benefits.

In an interview yesterday, Graham questioned whether the new monitoring program would work. "It will not sufficiently reduce the use of Accutane for less-severe forms of acne," said Graham, a drug-safety officer.

"A restricted distribution system should have been in place 15 years ago, and FDA scientists from both the drug safety office and the [drug] reviewing division were urging that it be adopted."

It is fairly common for regulators to restrict access to powerful drugs, and patient registries are a standard tool for closely monitoring safety. But a computerized system involving so many players is new territory for the FDA.

"This is a system long in the works, and many would say it is long overdue," said Dr. Sandra Kweder, deputy director of the FDA's Office of New Drugs. "The responsibility that fetuses not be exposed to this medicine is enormous, and is shared by everyone who participates" in distributing, prescribing or taking the drug.

About 100,000 prescriptions a month are written for Accutane or its generic equivalent, isotretinoin. Although the FDA says it should only be used to treat a disfiguring condition known as severe recalcitrant nodular acne, doctors are free to prescribe it as they judge best.

Graham said an estimated 3,000 to 4,000 women a year get pregnant while taking Accutane, and most opt to have abortions.

The Associated Press contributed to this report