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Group demand curves for cocaine (top) and remifentanil (bottom) prior to morphine administration (closed circles, solid lines), 3 hr after daily morphine (open triangles, dashed lines), 20.5 hr after daily morphine (closed squares, dotted lines), and 4 to 5 weeks following termination of daily morphine (open squares, dotted-dashed lines). Data points represent the group means.
