COMMENT The authors are to be commended on this study. It appears that they resourcefully took advantage of the M shortage from a few years ago to compare the clinical efficacy of spinal hydromorphone (HM) against morphine (M). Despite the relatively small numbers and the retrospective nature of this trial, the small differences they found between the drugs have the ring of clinical truth. Relative systemic potency reports between these 2 drugs range from 4 to 8:1 (HM:M). One early study sets it as high as 10:1.1 However, studies of neuraxial HM were scant until recent times. These authors chose a relatively high dose of spinal HM (0.04mg). Their results, although statistically not different between drugs, tended to show slightly higher side effects for HM over M, slightly less analgesia and shorter duration. A larger study population might find these differences to be real. Our own unpublished data with epidural HM after cesarean section found that it was not as clinically effective as M analgesia. This may have been because we used a relatively lower dose of 0.6-0.7mg HM compared to 4mg epidural MS. One final comment: Cost administrators (pharmacy) may like this study when confronted with another morphine shortage.