Study objectives: γ-Hydroxybutyrate (GHB) is a drug of abuse that is physically and psychologically addictive, with a withdrawal syndrome that may be lethal. The nature and course of GHB addiction has never been described in clinical literature. In addition to use of GHB as a recreational drug, GHB analogs (precursor chemicals that are rapidly metabolized to GHB when ingested) were sold as safe, natural, and nonaddictive "dietary supplements" for bodybuilding, weight loss, depression, insomnia, anxiety, and other purported health benefits, resulting in a diverse population of users and addicts. As supplements were regulated, analogs, which are used extensively in industry, were then sold as "all natural cleaners," "solvents," and "plant hormones." We seek to characterize GHB addiction and withdrawal. Methods: We collected emergency department (ED) and hospital records for treatment of GHB withdrawal, administered detailed initial and follow-up questionnaires, and conducted 2-hour interviews with a convenience sample of GHB addicts. We recruited participants through clinician contacts and through advertisement on the Project GHB Web site, which provides information on GHB and GHB addiction. Participants were screened by e-mail and telephone to ensure that they met at least 3 of 7 standard criteria listed in the <i>Diagnostic and Statistical Manual (DSM)-IV</i> for determination of drug dependence. Participants included active addicted users and recovering addicts. Informed consent was obtained according to institutional review board guidelines. We used descriptive statistics for data analysis. Here we present only general data from the initial questionnaire. Results: Forty-eight participants completed the questionnaire. Thirty-three participants were recruited through the Project GHB Web site and 15 through clinician contacts and participant referrals. Thirty-three participants met all 7 of the <i>DSM-IV</i> criteria for addiction, with a mean of 6.4 criteria fulfilled. Forty-one participants were from the United States (15 states), and 7 were from other countries (1 Canada, 3 England, 1 Scotland, 2 Australia). Thirty-two participants were men, and 16 were women. Ages ranged from 19 to 57 years, with a mean age of 32.9 years. Forty-seven participants were white, and 1 was Japanese-American. Eleven participants had pursued or completed high school education, 5 had technical training, 28 had 1 to 4 years of college education, and 4 had pursued or completed graduate studies. Thirty-five participants were employed, 5 were unemployed, and 8 were students. Twenty-nine participants began use of GHB/analogs for recreation, and 19 participants began use for purported health benefits, including sleep (44%); self-treatment of depression (31%), anxiety (31%), social anxiety (27%), and addiction (13%); weight loss (29%); energy (29%); and bodybuilding (23%). Many used multiple products, depending on availability, including "supplements" (30 used from 1 to 18 "supplements") and "solvents" (27 used an array of "cleaners," "solvents," and industrial chemicals). Twenty-two participants made their own GHB 1 or more times. Weekly cost of GHB/analogs ranged from less than $5 to $600. Earliest use of GHB/analogs was in 1989 and the mean length of addictive use was 24.4 months, ranging from 1.5 to 6 years. Initial individual dose size ranged from 0.5 to 4 g, with a total daily dose of 0.75 to 10 g; many did not know their exact dose, however. Individual dose size during periods of heaviest use ranged from 1 to 7 g, with a daily total ranging from 16 to 120 g. Thirty-eight participants who experienced physical withdrawal described peak dosing as round-the-clock, 7 days per week. However, 9 participants experienced physical withdrawal symptoms on less frequent dosage regimens; 3 described experiencing withdrawal symptoms on 2 to 3 doses daily. Four addicts knew that GHB was physically addictive before they began use, 5 learned of risk of physical dependence while using but not yet dependent, 14 learned when they began craving it, 2 learned when they sought medical help for treatment of withdrawal, and 3 learned when they went through detoxification. Eighteen participants presented 1 or more times (range 1 to 4 visits) to an ED for treatment of withdrawal, and 24 presented 1 or more times (range 1 to 8 visits) to an ED for treatment of GHB/analog intoxication. Conclusion: GHB is physically and psychologically addictive, and addicts represent a diversity of backgrounds, reasons for use, and knowledge of addictive risk. Emergency physicians need to be aware of GHB addiction and withdrawal.