History and Objectives: Considering the significance of analgesia and lower complications following surgical operations and the existence various and sometimes reports controversial reports on the efficacy of addition of fentanyl and for comparison of its effect, this study was carried out on patients under thoracotomy in Masih Daneshvari hospital.

Materials and Methods: The clinical trial, two-blind strategy of this study was performed on 74 patients and cases with contraindication for drugs were excluded from the study. Control group received morphine (0.5 mg/kg) and experimental group received a mixture of morphine and fentanyl. The intensity of pain was measured using verbal pain scoring and they were followed up for post-operative complications for 48h and data were statistically analyzed.

Results: From each group, 7 cases were excluded and study was carried out on 60 cases. In this regard, 31 cases were in control group and 29 cases were in experimental group. Both groups were similar regarding age and gender. Complications rate was 71% (22) in control group and 48.3% (14) in experimental group (P<0.07). There was a complication rate of 92.3% and 55.5% in female cases of control group and experimental group respectively. Meanwhile, duration of unexpected analgesia in control group was 8±4.8 and in experimental group was 9.03±4.5 h. in addition, duration of unexpected analgesia for control and experimental groups were 2±4.8 and 5±4.5 h respectively.

Conclusion and Recommendations: Simultaneous use of fentanyl and morphine could reduce the complications and extension of analgesia. Therefore, it is recommended to carry out further studies using fentanyl.