Pain control becomes poor in some cases after opioid switching from oxycodone tablet (OXC) to fentanyl patch (FP). However, fewer studies on risk factors have been reported. In this study, we surveyed the states of pain control (PC) and opioid administration, patient background, laboratory test values, and concomitant drugs retrospectively in 86 patients switching from OXC to FP between June 2010 and April 2018 in Mazda Hospital and Hiroshima Prefectural Hospital. The subjects were divided into 2 groups based on the median number of days to the initial dose increase after switching to FP. Between the early (<7.5 d) and late (≥7.5 d) increase groups, a significant difference was noted in the presence or absence of liver metastasis (LM), concomitant drugs with a high protein binding rate (CDHPBR), and the state of PC before and after switching to FP ( p < 0.05). Binary logistic regression analysis showed the presence of CDHPBR, absence of LM, and poor PC after switching were risk factors for early dose increase (presence of CDHPBR: odds ratios (OR), 3.30, 95% confidence interval (CI), 1.09–9.98; presence of LM: OR, 0.31, 95% CI, 0.10–0.93; good PC: OR, 0.23, 95% CI, 0.07–0.79, respectively). The initial dose increase after switching to FP was earlier in patients with CDHPBR and/or without LM than those without CDHPBR and with LM ( p < 0.05, log-rank test). It was suggested that the analgesic effect of FP after switching from OXC is likely to be insufficient in patients treated with CDHPBR and patients without LM.