Sometimes in science, as in politics, connections arise that may at first glance appear to be strange bedfellows. That might be the natural first impression of a potential association between chemical intolerance and addiction. But although the conditions are manifested by behaviors that appear to be polar opposites—substance avoidance (or abdiction, as some are beginning to call it) by the chemically intolerant, and compulsive substance use by the addicted—there is evidence to suggest that, biologically, they may actually have much in common. That was the concept behind “Addiction and Chemical Intolerance: A Shared Etiology?” This conference, held 19–20 September 2005 in Research Triangle Park, North Carolina, was the first scientific meeting to be cosponsored by the NIEHS and the National Institute on Alcohol Abuse and Alcoholism (NIAAA). It was also the first time researchers from the fields of environmental health and addiction convened to explore common ground and potential collaborations. “The idea of hosting a conference on chemical intolerance and addiction stems from a long history of individual physicians’ reporting observations on patients that looked like addiction to chemicals, foods, caffeine, or alcoholic beverages,” explained conference chair Claudia Miller, a professor and researcher in environmental medicine at The University of Texas Health Science Center at San Antonio. “There is a striking resemblance between the symptoms and responses to substances reported by chemically intolerant patients and individuals addicted to drugs or alcohol.” Firm numbers on addiction and chemical intolerance are hard to come by, in part because both conditions often go undiagnosed. Approximately 67% of all Americans drink alcohol, yet 90% of the alcohol is consumed by only 30% of the population, said NIAAA director Ting-Kai Li in his keynote address. In the latter half of 2003 (the most recent year for which figures are available), there were 627,923 drug-related emergency room visits in the United States, according to the Drug Abuse Warning Network of the U.S. Substance Abuse and Mental Health Services Administration. As for chemical intolerance, epidemiologic figures compiled and reported at the meeting by William Meggs, a professor of emergency medicine at East Carolina University, suggest the prevalence of the condition (self-reported) to be approximately 12% of the U.S. population, with approximately 4% self-reporting as “seriously affected.” Miller contends that addiction and chemical intolerance represent divergent physiologic responses to a shared underlying disease mechanism she calls toxicant-induced loss of tolerance (TILT). In TILT, a chemical exposure—either acute or chronic and low-level—initiates sensitization to even small amounts of structurally diverse chemicals found in foods, drugs, alcoholic and caffeinated beverages, pesticides, mold toxins and other elements of indoor air, implanted devices, solvents, cleaning chemicals, and more. Thereafter, when affected individuals are exposed to everyday “triggering” substances such as foods, traffic exhaust, or fragrances, they report multisystem symptoms including headache, nausea, difficulty breathing, muscle spasms, and rashes. The fact that different people exhibit different constellations of symptoms has made it difficult to conduct epidemiologic studies or arrive at a case definition, Miller says. In the past, these difficulties have led some observers to speculate that chemical intolerance is psychogenic in origin. As she outlined in her presentation to the approximately 120 attendees, Miller postulates that the TILT mechanism can lead to either abdiction or addiction, with both behaviors intended to avoid unpleasant withdrawal symptoms. She further proposes that TILT may underlie a wide variety of chronic diseases that are increasing in prevalence worldwide, such as asthma, autism, chronic fatigue syndrome, fibromyalgia, and depression. (She described these proposals in depth in an article in the January 2001 issue of Addiction.)