Physiological and behavioral responses to forced methamphetamine consumption and abstinence. (a) Mean (± SEM) daily methamphetamine intake during the 2-week period of forced methamphetamine consumption prior to abstinence, showing escalation of intake. (b) Mean (± SEM) body weights, measured every 3-4 days over the course of the 6-week long experiment. n = 8 animals/group. (c) Mean (± SEM) overall withdrawal signs, recorded every 12h for 72h following removal of methamphetamine bottles. * p < 0.05, ** p < 0.01, *** p < 0.001, indicate significant differences between methamphetamine pre-exposed and not-pre-exposed groups.