- The aversive properties of acute naloxone-precipitated morphine withdrawal were examined in the taste reactivity paradigm. Acute naloxone-precipitated withdrawal paired with sucrose solution established conditioned active rejection of the sucrose solution. Active rejection of sucrose was observed when naloxone was administered both 1 h and 22 h after morphine. When the stimulus properties of morphine were present during the conditioning trial, the conditioned sucrose aversion was only expressed when the rats were tested in the same drug state in which they had learned the aversion. However, when the stimulus properties of morphine were not present during conditioning, the aversion was expressed in the absence of the morphine state. The results suggest that palatability shifts can be conditioned to sucrose paired with acute morphine withdrawal.