Chronic pain patients being treated with certain opioid and non-opioid medications had significantly lower serum concentrations of free testosterone (fTe) and free estradiol (fE2), highlighting the potential endocrinologic side effects of these drugs. These were the findings of a new study published in the journal Drug Testing and Analysis.

Researchers measured the concentration of fTe and fE2 in serum and plasma samples from adults taking opioid and non-opioid medications (male: n=120, 21–84 years, median age 53; and female: n=120, 22–95 years, median age 51.5). The measured concentrations were compared to an age and gender matched control group, not positive for these medications. Measurements were made via the equilibrium dialysis-liquid chromatography-tandem mass spectrometry. 

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Results showed a reduction in concentrations of fTe in male samples positive for hydrocodone, oxycodone and morphine but not in samples positive for methadone, fentanyl, tramadol, and the non-opioid medications gabapentin and pregabalin.

When compared with age-matched controls, women between 48–55 years had reduced fE2 concentrations in samples positive for tramadol, fentanyl and gabapentin (P= 0.0243, 0.0045 and 0.0050, respectively). 

Post-menopausal women receiving gabapentin were found to have significantly lower fE2 levels (P=0.0050) compared with the controls in the same age range, leading the authors to suggest that the use of gabapentin could possibly be negating the effects of any estrogen replacement therapy.

The researchers also highlight the finding of pregabalin having no significant effect on fTe or fE2 levels as noteworthy, given the lack of current knowledge on the effects of pregabalin on sex hormone levels.

The authors concluded that “measurement of free hormones in pain medication users could be important in determining their association with sexual function.”

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