The Effect of Preoperative Cannabis Use on Postoperative Pain Following Gynaecologic Oncology Surgery

Objective: To determine whether cannabis users have different pain scores after gynaecologic oncology surgery than non-cannabis users. Methods: A retrospective chart review was completed for 654 patients who underwent gynaecologic oncology surgery during a 2-year period. The primary outcome was postoperative pain at 12 and 36 hours after surgery using an 11-point pain scale. Secondary outcomes included opioid consumption, length of hospital stay, opioid side effects, and sleep disturbance. Results: Of all patients included in this study, 64 used cannabis and 590 did not. Propensity score matching and list-wise deletion identified 57 matched pairs. Pain scores were significantly higher at 12 hours (P < 0.001) and 36 hours (P =0.002) after surgery in cannabis users (median pain scores 6 [IQR 5–7]) and 5 [IQR 4–7], respectively) than non-users (median pain scores 4 [IQR 3–6] and 4 ([IQR 2–5], respectively). Median opioid consumption was significantly higher at 12 hours (P = 0.039) and 36 hours (P = 0.044) after surgery in cannabis users (oral morphine equivalent [OME] 20 [IQR 10–40] mg and OME 40 [IQR 10–100] mg, respectively) than non-users (OME 10 [IQR 5–20] mg and OME 30 mg [IQR 7.5–50] mg, respectively]. Sleep disturbance was significantly higher in cannabis users (odds ratio 3.31; P = 0.009). Conclusions: After gynaecologic oncology surgery, patients who used cannabis preoperatively had higher postoperative pain scores, higher opioid use, and more sleep disturbance than non-users. This suggests that preoperative cannabis use is a risk factor for postoperative pain.