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. Author manuscript; available in PMC: 2020 Sep 1.
Published in final edited form as: J Pain. 2019 Mar 7;20(9):1040–1047. doi: 10.1016/j.jpain.2019.03.002

Figure 5. Lack of tolerance to morphine and fentanyl combined following pretreatment with morphine or fentanyl alone.

Figure 5.

(a) Twice daily microinjections of morphine (5 μg/0.4 μL) or fentanyl (5 μg/0.4 μL) for two days did not cause tolerance to the combination of morphine+fentanyl. (b) Twice daily microinjections of morphine+fentanyl for two days caused a rightward shift in the combined dose-response. (N = 8/group)