WASHINGTON (AP) -- A version of the date-rape drug GHB significantly helps a dangerous complication of the sleep disorder narcolepsy, the government ruled in deciding that certain patients now can buy it.

But the Food and Drug Administration's approval of the version named Xyrem late Wednesday came with some of the most severe restrictions ever imposed on a medicine. The agency's move, nevertheless, carves out a single medical use for an otherwise illegal chemical.

Throughout the 1990s, the government had cracked down on illegal GHB use - abused as a party drug, sex and athletic enhancer and, because it can knock people out, a date-rape drug. Several dozen deaths are blamed on the chemical. But GHB was hard to stop because it was easy for people to mix up with some common chemicals.

Now the maker of the FDA-approved version, Orphan Medical Inc., will have to balance how to get GHB to patients who need it while at the same time not letting it fall into the wrong hands.

"No system, I believe, is foolproof, but there will be very close tabs" kept on every GHB shipment, said Dr. Russell Katz, FDA's neurologic drugs chief.

Narcolepsy is marked by recurring episodes in which patients suddenly fall asleep from a few seconds to an hour. GHB doesn't treat that symptom. However, anywhere from 20,000 to 50,000 narcolepsy patients also suffer cataplexy, a muscle-weakness complication that can cause them to collapse without warning.

Orphan Medical's version of GHB, to be sold under the brand name Xyrem, marks the first FDA-approved treatment for cataplexy. Studies suggest Xyrem (pronounced Zy-rem) could reduce cataplexy attacks by up to 70 percent.

Originally developed as a surgical anesthetic, GHB was pulled off the market because of side effects: it depresses breathing and can cause coma, even kill.

Then in 1990, some companies began selling it as a dietary supplement, and use as a recreational drug took off. Colorless and odorless, it made headlines when people slipped it into drinks, knocking out victims who often had no memory of what happened.

By the mid-90s, the government had declared any GHB use outside of FDA-sanctioned clinical trials illegal. A 2000 law toughened penalties so abusers or distributors could face a prison term. The Drug Enforcement Administration has blamed GHB for at least 58 deaths and 5,700 recorded overdoses since 1990.

But despite the abuse, scientists were studying reports that by altering the quality of narcoleptics' nighttime sleep, GHB might improve some of the disorder's daytime symptoms, including cataplexy.

Wednesday, the FDA concluded Xyrem, a liquid version of GHB, indeed helps cataplexy.

But patients who want to use it face a host of restrictions. Every doctor who prescribes Xyrem must enroll on an FDA-monitored registry that also will record the name and medical progress of every patient who takes it.

Orphan Medical will hire one pharmacy to distribute Xyrem, sending it by Fed-Ex to the homes of properly registered patients who have certified they understand how to use it and the penalties for abuse.

The patient must sign for each shipment - reports of lost or missing drug will immediately trigger an investigation.

Patients or doctors who divert the drug for illegal use can face jail, Katz warned.

There are side effect warnings for patients who use Xyrem correctly, the FDA cautions - the same breathing problems abusers faced, especially if patients use Xyrem together with alcohol or other central nervous system depressants. Other side effects are rare but include bedwetting, sleepwalking and confusion.

The FDA will monitor the patient registry for reports of side effects, and urged doctors to report any problems by calling 1-877-67-Xyrem.

Orphan Medical said it will begin sales by year's end but did not release a price.

Copyright 2002 The Associated Press. All rights reserved.