ObjectiveSexual dysfunction and low testosterone levels have been observed previously in males with chronic noncancer pain treated with intrathecal opioids. To investigate the hypothesis that intrathecal opioids suppress the hypothalamic-pituitary-gonadal axis, a prospective nonrandomized investigation of the function of this axis was undertaken.DesignTen males with chronic noncancer pain were evaluated for clinical and biochemical evidence of hypogonadism at baseline and during the first twelve weeks of intrathecal opioid therapy.ResultsIntrathecal opioid administration resulted in a significant (p<0.0001) reduction in serum testosterone, from 7.7 ± 1.1 (mean ± SEM) nmol/L at baseline to 2.0 ± 0.7, 2.8 ± 0.5, and 4.0 ± 0.9 nmol/L at 1, 4, and 12 weeks, respectively. This was associated with a reduction in libido and potency. Luteinizing hormone and follicle-stimulating hormone levels remained within reference ranges, indicating central rather than peripheral suppression.ConclusionsAdministration of intrathecal opioids may result in hypogonadotrophic hypogonadism. As part of the consent for therapy process, patients should be informed about this effect and its management. With long-term intrathecal opioid administration, the hypothalamic-pituitary-gonadal axis should be monitored. Where indicated, testosterone replacement should be undertaken to improve sexual function and prevent the potential metabolic effects of hypogonadism, in particular, osteoporosis.