Xerostomia as a Rare Adverse Effect of Low-Dose Oral Minoxidil: A Case Report With Recurrence After Rechallenge

Low-dose oral minoxidil (LDOM) is an emerging option for the treatment of female pattern hair loss (FPHL), generally well tolerated at doses under 1 mg/day. We report a rare adverse event of significant xerostomia in a 74-year-old woman with Hashimoto's thyroiditis, receiving 0.5 mg/day of minoxidil for FPHL. After 5 months of therapy, she developed progressively worsening dry mouth that significantly impaired speech and social interactions. Cardiologic and rheumatologic evaluations excluded other causes, including Sjögren's syndrome. Symptoms completely resolved after drug withdrawal and promptly recurred after a single rechallenge, supporting a causal relationship. Subsequent treatment with topical minoxidil was well tolerated and maintained the clinical improvement in hair density. This case highlights a potential, underrecognized adverse effect of oral minoxidil.