Pattern of Methamphetamine Use and the Time Lag to Methamphetamine Dependence.

OBJECTIVES: Use of methamphetamine (MA) commonly co-occurs with the use of other substances. The present study aims to examine substance initiation patterns of other substances, including alcohol, nicotine, inhalants, and cannabis (OTH), in MA users and its consequence on the time lag of MA dependence.

METHODS: Sociodemographic, environmental, and clinical data were obtained from MA users at a Thai substance treatment center. The Semi-Structured Assessment for Drug Dependence and Alcoholism was employed to diagnose drug dependence.

RESULTS: Of 991 MA users, 52.6% were males, and the average age was 26.8 ± 7.1 years. The mean age of first MA use (18 years) was greater than the mean age of first use of alcohol (17 years), nicotine (16 years), and inhalants (15 years) (P < 0.001), but was comparable with the mean age at the first use of cannabis (P > 0.05). Family history of MA use and nicotine dependence were associated with early MA onset. Participants who used MA as their first drug (MA>OTH) were more likely to be female and less likely to smoke intensely and to be exposed to severe traumatic events than those who used MA later than other substances (OTH>MA). The time lag from age at onset of MA use to MA dependence was shorter in OTH>MA than in MA>OTH (3 vs 5 years; χ = 5.7, P = 0.02, log-rank test).

CONCLUSIONS: A higher proportion of women was observed in MA>OTH than in OTH>MA. The use of other substances before MA increases the individual's vulnerability in shortening the interval between age at onset of MA use and MA dependence in a substance treatment cohort.