The ICD-9 coding framework does not distinguish between methamphetamine and other amphetamines. However, it is likely that the ICD-9 amphetamine-related codes can serve as reasonable proxies for methamphetamine-related conditions based on two lines of evidence. During the time frame of our study, almost all amphetamine-related admissions to substance abuse treatment in California were specifically for methamphetamine. From
1992 through 2000, there were 225,999 primary amphetaminerelated inpatient and outpatient treatment admissions to publicly funded substance abuse treatment programs in California,and methamphetamine accounted for 96.4% of these episodes(19). Also, in California, Arizona, and Nevada, federal legislation to control methamphetamine precursors in order to reduce the manufacture and supply of methamphetamine produced statistically significant reductions in inpatient hospital admissions with the methamphetamine-related ICD-9 diagnostic codes we used in our study (20)—a pattern supporting the use of the ICD-9