Human drug discrimination and multiple chemical sensitivity: caffeine exposure as an experimental model.

Multiple chemical sensitivity is a controversial diagnosis. Rigorous, controlled, laboratory-based research can reduce this controversy and lead to potential clinical confirmatory tests. The literature on human caffeine discrimination provides a rigorous methodology that can address reports that patients who suffer multiple chemical sensitivity (MCS) are sensitive to usually well-tolerated chemical doses; the studies require patients to discriminate caffeine from placebo under double-blind conditions. Several issues relevant to the conduct of caffeine discrimination studies using MCS patients as subjects are addressed; these issues include study design, determination of safe and tolerable training doses, and discrimination training. Such research will benefit patients and clinicians dealing with a diagnosis of MCS.