Fig. 5. Mean phantom limb pain (95% confidence interval) and stump pain intensity (visual analog scale [VAS] score [0 = no pain, 100 = worst pain possible]) at baseline and during 28 days of treatment in slow and fast cytochrome P450 2D6 metabolizers receiving tramadol. *P < 0.01 fast  versus slow metabolizers in first week by analysis of variance between groups (analysis of variance).