Gastrointestinal Side Effects of Low-Dose Oral Minoxidil in Patients with Alopecia: An Underrecognized Association

Introduction: Low-dose oral minoxidil (LDOM) has become an increasingly used therapy for alopecia. While dose-dependent hypertrichosis is the most common side effect, gastrointestinal (GI) adverse effects are plausible due to smooth muscle relaxation, but they have not been systematically reported in clinical studies. Objectives: To investigate the frequency and characteristics of GI adverse effects in patients treated with LDOM for alopecia. Methods: We conducted a prospective observational study at a trichology unit including patients attending their second consultation after initiating oral minoxidil between May and August 2025. A structured questionnaire assessed new GI symptoms, temporal relationship with treatment, and concomitant medication use. Results: Among 302 patients (218 females, 84 males; mean age 46 years), 22 (7.3%) reported new GI symptoms. The most frequent symptoms were flatulence (N=18), heartburn (N=13), abdominal distension (N=12), abdominal pain (N=10), and aerophagia (N=7). Symptoms resolved after discontinuation in 15 of 16 cases and recurred after reintroduction in 14 of 15. A dose-response association was observed (mean dose in patients with GI symptoms 2.7 ± 1.6 mg vs. 1.3 ± 1.2 mg in those without, P=0.01). GI side effects were more common in males (15.5%) than in females (4.1%, P<0.001) and in patients treated with concomitant vasodilators (25.6% vs. 4.6%, P<0.001). Conclusions: GI complaints, particularly aerophagia, abdominal pain or distension, and flatulence, appear to be underrecognized adverse effects of LDOM. Although generally mild, these symptoms may affect adherence and quality of life. Clinicians should inquire about GI complaints, especially in male patients receiving higher doses or concomitant vasodilators.