A quantitative review of the ubiquitous relapse curve

Abstract

The primary goal of this study is to ascertain whether relapse to drug dependence, in terms of continuous abstinence assessment, exhibits a typical pattern that can be characterized by a common quantitative function. If the relapse curve is indeed ubiquitous, then some underlying mechanism must be operating to shape the curve that transcends variables such as drug class, population, or treatment type. Survival analyses are performed on 20 alcohol and tobacco treatment studies using the proportions of individuals remaining abstinent after a period of initial abstinence. Several parametric models of relapse are compared, and the results demonstrate that a log-logistic distribution is the most accurate reflection of the available data and the basic shape of the relapse curve is uniform. In most reports examined, the rate of relapse decelerates after initial abstinence has been achieved, and therefore, the amount of accumulated time abstinent may be the transcending variable that operates to shape the relapse curve.

Figure 1

A visual comparison of the predictions of the four different parametric survival models.

Figure 2

Probability plots for studies that involved either alcohol (left) or nicotine (right) relapse.

Figure 3

The hazard functions for the log-logistic distribution for alcohol (left) and nicotine (right) studies.

Figure 4

Analysis of continuous abstinence from all 20 studies. On the occasion that only graphical data were available, digiMatic software (1995, FEB Software) was utilized to approximate percent-abstinent data points.