Gabapentinoid anticonvulsants are standard treatment for neuropathic pain and are often combined with opioids for treating cancer. It is assumed that this combination may heighten somnolence and respiratory depression due to the inhibitory effects of opioids on the central nervous system. Although pregabalin, a gabapentinoid, is known to increase somnolence frequency during opioid therapy, whether mirogabalin exerts similar effects on somnolence frequency under opioid therapy remains unknown. This study examined the signals of somnolence and respiratory depression in response to pregabalin and mirogabalin use by utilizing data from the Japanese Adverse Drug Event Report database and assessed their interaction with strong opioid analgesics.