Declining rate of substance abuse throughout the month

PURPOSE: The timing of federal disbursements of welfare, disability, and military benefits may be associated with monthly patterns of substance abuse. We assessed whether this association was reflected in the pattern of psychiatric presentations to an emergency room.

SUBJECTS AND METHODS: We conducted a retrospective, case-control study of 12,904 patient presentations to an urban emergency department for psychiatric reasons during a 7-year period. Cases were defined as patients (n = 2,403) given a primary diagnosis of substance abuse. Controls included patients (n = 10,501) with a primary diagnosis of another psychiatric illness. We calculated the “boundary effect” (R = 100 times the number of presentations during the first week of the month divided by number of presentations during the last week of the preceding month) for each month, and averaged these values across months to determine overall effects.

RESULTS: The boundary effect was stronger for patients with primary substance abuse disorders (R = 134, 95% confidence interval [CI] = 118 to 151) than for patients with other psychiatric disorders (R = 106, 95% CI = 100 to 112; P <0.001). Weekly presentations for substance abuse declined consistently throughout the month (P = 0.01), and declined significantly more than the incidence of other psychiatric presentations (P = 0.005). These effects remained, after adjusting for fluctuations in presentations around holidays and the new year. The lunar cycle did not influence the incidence of presentations.

CONCLUSION: Our results confirm that substance-related morbidity is highest at the beginning of the month and declines thereafter, corresponding to the availability of disposable income from monthly checks.