The case history of a 17-year-old girl with sudden onset of theophylline toxicity and a serum theophylline concentration of 63 micrograms/ml is presented. A change in theophylline elimination was not sufficient to explain this observation. Subsequently, the patient admitted to recent self-medication with several over-the-counter medications and illicit drugs. Although the etiology of theophylline toxicity in this patient could not be defined, several theories are proposed. Included is a discussion of possible interactions of illicit drugs with asthma medications and a summary of personality characteristics associated with a high potential for drug abuse.