A 48-year-old man on long-term sustained-release oral morphine for chronic back pain presents with decreased libido, erectile dysfunction, and fatigue. Laboratory tests show low serum testosterone with low-normal LH and FSH. Which mechanism best explains this opioid-induced endocrinopathy?

• A Direct cytotoxic effect of opioids on Leydig cells in the testes
• B Increased aromatase activity converting testosterone to estradiol
• C Opioid-induced suppression of GnRH secretion from the hypothalamus ✓
• D Opioid-mediated increase in prolactin causing secondary hypogonadism

Explanation

Chronic opioid use suppresses hypothalamic GnRH release, leading to reduced pituitary LH and FSH secretion and secondary hypogonadism. This is the most common opioid-related hormonal disturbance. Option A is incorrect because opioids do not directly damage Leydig cells. Option B is not the primary mechanism. Option D describes hyperprolactinemia, which is more typical of antipsychotics.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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