"Yes, people are right. Caffeine is addictive.", NYT, 5 Oct 94, p. B9. Researchers have found that some people are addicted to caffeine in the same way that others are addicted to cigarettes or alcohol. They found that even when caffeine threatens a person's health, that person may not be able to give up the drug. Also, some of those who eliminate caffeine from their diet for a few days may not be able to function as effectively during those days as they did during days in which they consumed caffeine. "Caffeine dependence syndrome: Evidence from case histories and experimental evaluations", E. C. Strain et al., JAMA, 5 Oct 94, Vol. 272, No. 13, pp. 1043-1048. Background: Caffeine is the most widely used psychoactive substance in the world. In low doses (20 to 200 mg), positive effects are experiences, including added alertness and energy. In higher doses (200 to 800 mg), negative effects are also prevalent, including nervousness and anxiety. Studies examining the relationship between caffeine and various illnesses such as cancer generally have failed to find that typical daily doses of caffeine are related to these illnesses. Objective: The purpose of this study was to asses volunteers who reported problems associated with caffeine use; the subjects were then diagnosed in terms of caffeine dependence based on the criteria for substance dependence from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). Kind of study: Case-control study (Case-series evaluations) Outcome measurements: Main outcome measure: Diagnoses made be a psychiatrist using an interview which included a section on caffeine dependence using criteria for DSM-IV substance dependence. Secondary Outcome Measure: Double-blind caffeine- withdrawal evaluation. Subjects: Volunteers who believed that they were psychologically or physically dependent on caffeine. 99 people were included in the main outcome measure, while 11 of these 99 people were part of the secondary outcome measure. Setting: An academic research center in the Department of Psychiatry and Behavioral Sciences at the John Hopkins University School of Medicine, Baltimore, Md. Treatments: Subjects were labeled caffeine dependent or not caffeine dependent according to the some of the classifications of dependancy from DSM-IV. Of the caffeine dependent subjects, treatments included caffeine pills and placebos. Treatment assignment: Subjects that were classified as caffeine dependent were used for the second part of the study. Each person participated in a two 2-day study periods, and they received, in random order, either caffeine in an amount equal to their individual daily caffeine consumption or a placebo. Control variables: None Blindness: No blindness in the first part of the study. In the second part of the study, double blindness existed. Population: Volunteers, age 21 to 50. Self-identified adults who believed they were dependent on caffeine. Statistical methods used: Comparison of average daily intake of caffeine in 16 people who were classified as dependent on caffeine. Median caffeine intake of the 16 subjects. Percentages of people who experienced different effects when daily caffeine intake was eliminated. Two tables. (should I mention anything about the footnotes on page 1046?) Stated conclusions: Of 99 subjects screened for the study, 16 were identified as having a diagnosis of caffeine dependence. Of these sixteen people, the median daily caffeine intake was 357 mg. 94% reported withdrawal, 94% reported continued use despite experiencing a physical or psychological problem associated with its use, 81% reported the inability to cut down on use, and 75% reported tolerance. 11 subjects were a part of the double-blind caffeine-withdrawal evaluation, and 82% (9) showed objective evidence of caffeine withdrawal. 8 of the subjects reported functional impairment. Nonresponse: Of the sixteen people who were classified as caffeine dependent, four declined to continue in the study and one became ineligible to participate as a result of a development of hypertension during the time the study was being conducted. Difficulties of generalizing to the real world: The subjects volunteered to be a part of the study; this group may differ in general characteristics from the entire world population. Also, those that were diagnosed as caffeine dependent had higher rates of phychiactric diagnoses (substance abuse, mood disorder, etc.) than that of the U.S. population as a whole; this may mean that those who have had other psychiactric problems in the past are more likely to become caffeine dependent, so there may be other factors in the determination of caffeine dependence. How does this relate to the rest of the scientific literature: This study agrees with previously held beliefs that caffeine use can become addictive. Previous studies also have shown that subjects can be intoxicated with the excessive use of caffeine and that caffeine can produce a withdrawal syndrome when subjects stop habitual use.