While clinical studies suggest depressed patients may be more vulnerable to pain, experimental research is equivocal. This meta-analysis aimed to clarify whether depression is associated with altered pain perception in response to noxious stimulation and to identify factors that might influence this association. A search of major electronic databases was conducted to identify experimental studies investigating pain response in depressed participants vs. healthy controls using established pain outcome measures. Random effects meta-analysis of standardized mean differences was conducted on data from 32 studies (N=1,317). For high-intensity noxious stimulation, overall pain tolerance was similar across depressed and control groups (Hedge’s g=0.09, p=0.71, studies=10). For low-intensity stimulation, a small, but statistically significant higher mean sensory threshold (g=0.35, p=0.01, studies=9) and pain threshold (g=0.32, p=0.02, studies=25) was observed in depressed participants, suggesting diminished pain. However, considerable heterogeneity in the direction and magnitude of effects was observed, indicating a likely condition-specific impact of depression on pain. Subgroup analysis found that pain threshold/tolerance was increased in depression for exteroceptive (cutaneous) stimulation but decreased for interoceptive (ischemic) stimulation, but that substantial heterogeneity remained. Overall, results provide some support for altered pain processing in depression, but suggest this link is dependent upon modality and additional, unidentified factors.
This meta-analysis of experimental studies suggests potential effects of depression on pain perception are variable and likely to depend upon multiple factors. The contrasting pattern for ischemic vs. other noxious stimuli suggests that stimulus modality is a key factor, which could help explain discrepancies across clinical and experimental findings.