A muscle builder. A fat burner. A sleep aid. An aphrodisiac. A natural "high." Claims like those helped boost sales of gamma butyrolactone (GBL), a dietary supplement that the Food and Drug Administration asked manufacturers to recall last month because of at least 55 cases of serious illness, including users who suffered seizures, coma and respiratory arrest. At least one person has died after taking GBL, which the FDA considers a dangerous, unapproved drug. Sold over the Internet and in gyms and health food stores, products containing GBL gained popularity last year because the supplement produced the same effects as gamma hydroxybutyrate or GHB, a banned chemical cousin. Never an approved drug, GHB had attracted bodybuilders and wrestlers as an alternative to steroids for "bulking up" muscles, as well as recreational users intrigued by its odd combination of sedative and stimulatory effects on the brain. It also became notorious as a date rape drug. GHB's production and sale were banned in 1991 after it was linked to numerous cases of serious illness and some deaths. Last summer, cases like those associated with GHB--comas, unexplained seizures, people with dangerously slow heartbeats or breathing--began showing up in GBL users, said Mary Palmer, a toxicologist working on a large study of illness and poisoning in dietary supplement users. There are no reliable figures on how many people have taken GBL, whose primary use is as a solvent in products such as floor stripper, paint thinner and nail polish remover. It goes by various chemical names and is an ingredient in several dietary supplement products. (See box.) The similar symptom profile is easy to explain: GBL is chemically converted by the body into GHB, the banned drug. "The seemingly less worrisome supplement becomes converted into something that's very worrisome," said Gary I. Wadler, an associate professor of Clinical Medicine at New York University School of Medicine and lead author of a textbook on drugs and the athlete. Wadler said the recent popularity of GBL resembles the situation with androstenedione, another over-the-counter supplement taken by some athletes that the body converts into testosterone, a prescription hormone. In both cases, he noted, the laxity of the law regulating dietary supplements allows people easy access to substances that can act like powerful drugs and that may pose serious risks to their health. When the Dietary Supplement Health and Education Act was passed in 1994, reducing the FDA's authority to regulate supplements, "I don't think anybody envisioned this scenario as it's playing out," Wadler said. "It is time to revisit that act." The banned GHB has a dual action on the brain. Like cocaine, it stimulates nerve cells that respond to the chemical messenger dopamine, producing an excitatory effect. Like heroin, it activates natural opium-like substances within the brain, causing sedation. Taking GHB "is sort of like taking heroin and cocaine at the same time," Wadler said. The result can be a perplexing set of symptoms. Palmer recalled the case of a New York topless dancer. "She did her dance, got offstage and she dropped. She came into the emergency room in a coma." Doctors inserted a breathing tube. They discovered that her heart rate was 50--alarmingly slow. Then she developed an irregular heartbeat. When she woke up, she admitted that she had taken GHB. GBL apparently can produce a similar spectrum of effects. Arizona doctors reported the case last September of a 36-year-old man who was stopped for driving erratically and was found to be sweating, vomiting and lethargic. He acted drunk but tests for alcohol and illicit drugs were negative. He recovered within an hour and reported that he had taken two ounces of RenewTrient, a GBL-containing product. GBL never should have been marketed as a dietary supplement because it was a new ingredient that had been clearly shown to have dangerous effects in human and animal studies, said Annette Dickinson, vice president for scientific and regulatory affairs of the Council for Responsible Nutrition (CRN), a trade association representing about 100 supplement manufacturers. She noted that the companies selling GBL do not belong to her organization. "We don't see how anyone could reasonably conclude that it would be safe at the kind of levels that were recommended" on product labels, she said. Last Friday, the FDA announced that three manufacturers of GBL-containing supplements--G.H. Distributors Inc., Trimfast Group Inc. and Conan Corp./Castlewood Nutritional Systems--had agreed to the voluntary recall. The agency has sent letters to four other companies, warning of possible legal action against their products if they do not cooperate. Warning letters were sent to Alpha Earth Inc., Miracle Marketing Distributors and RenewTrient Research (all of Florida) and Advanced Athletic Nutrition of Roseville, Calif. Sanjay Sabnani, a spokesman for Trimfast, said the company is in the process of rounding up its Revivarant products from distributors. "We have never received any complaints from customers or health authorities," he said. Paul A. Cotton, a sports nutritionist and the head wrestling coach at Howard University, said GBL is "mildly popular," in the wrestling community, whose athletes often are attracted to substances that they believe will give them a competitive edge. He said he had counseled athletes who had tried GBL but hadn't encountered any cases of illness. They're "a little bit secretive about what they're taking," he added. Cotton said he warns his athletes that purity and manufacturing standards for dietary supplements have not been set by the government. "I kind of equate it to buying street drugs," he said. However, he predicted that news of the government recall of GBL may trigger a flurry of last-minute orders for the products over the Internet. "Those individuals in the gymnasium . . . always say, 'If it wasn't working, they wouldn't take it off the market,' " he said. GBL AT A GLANCE Name: Gamma butyrolactone, often called GBL. The supplement is commonly sold under the names of Renewtrient, Revivarant or Revivarant G, Blue Nitro or Blue Nitro Vitality, GH Revitalizer, Gamma G, Insom-X and Remforce. GBL may be an ingredient in additional products. It is also known by its chemical names 2(3h)-furanone dihydro, butyrolactone, 4-butyrolactone, dihydro-2(3H)-furanone, 4-butanolide, 2(3H)-furanone dihydro, tetrahydro-2-furanone and butyrolactone gamma. Marketing: Sold over the Internet, in some health food stores and some gyms and fitness centers. It comes in a liquid and powder form. Promoters claim GBL builds muscles, improves physical performance, promotes fat loss, enhances sex, reduces stress and induces sleep. Side Effects: Seizures, vomiting, slow breathing, slow heart rate, loss of conciousness. Reports of at least 55 adverse health effects have been reported to the Food and Drug Administration, including one death. Gamma butyrolactone is converted in the body to gamma hydroxybutyrate or GHB, which is a potent unapproved drug. To Report Problems: Call FDA's MEDWATCH at 1-800-332-1088. The FDA advises all consumers to dispose of any supplies they have of GBL. Source: Food and Drug Administration