Does prolonged oral treatment with sustained-release morphine tablets influence immune function?

Opioids such as morphine are the mainstay of acute and chronic pain treatment. The purpose of this study was to investigate the immunosuppressive effects of morphine in patients with pain syndromes. We investigated 10 patients with chronic pain syndromes undergoing treatment with oral sustained-release morphine (30-240 mg/d) before and after 1, 4, and 12 wk of treatment compared with healthy control subjects without morphine treatment. Immunological variables of the cellular and humoral immune axis showed that 1) total lymphocyte counts and the distribution of lymphocyte subpopulations, including helper T-cell/suppressor cytotoxic T-cell ratios (CD4/CD8 ratios), did not change compared with baseline or healthy control subjects; 2) proliferation of peripheral mononuclear cells (PMC) was not impaired by morphine treatment; 3) interleukin 2 production increased after 4 wk of treatment with morphine; and 4) immunoglobulin (Ig) production was reduced before initiation of therapy in pain patients and decreased further during morphine treatment, whereas Ig concentrations in the circulation remained at normal levels. These results indicate that treatment with oral, sustained-release morphine does not have a suppressive effect on overall PMC function. On the other hand, Ig production was impaired in patients with chronic pain and was further suppressed by morphine. Whether this suppression of humoral immune function has a clinical impact on the immune system as a whole remains to be determined. Implications: Treatment of patients with chronic pain with oral, sustained-release morphine does not influence cellular immune function, but it suppresses the already attenuated production of immunoglobulins.