Loperamide-induced hypopituitarism

Loperamide is the most commonly used antidiarrhoeal medication in the UK. We report a serious and hitherto undocumented adverse effect of chronic use in a 45-year-old man with inflammatory bowel disease. He presented to the endocrine clinic with fatigue and low libido; biochemical assessment revealed hypogonadism and adrenal insufficiency without any elevated adrenocorticotropic hormone. When symptoms allowed, loperamide was reduced and a short synacthen test (SST) showed a 'clear pass' with a normal peak cortisol of 833 nmol/L. Later, worsening diarrhoea necessitated an escalation in loperamide use again. While taking a daily dose of 15-20 mg (recommended daily maximum 16 mg) reassessment revealed a fall in peak cortisol on SST to 483 nmol/L, a subnormal response. Clinicians should exercise caution when relying on loperamide to manage their patients' chronic diarrhoea and remain mindful of the possibility of drug-induced life-threatening adrenal insufficiency.