Topical Minoxidil Side Effects: Incidence Rates Across Clinical Trials

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What the 48-week solution trials found

In a 48-week double-blind, placebo-controlled trial, 393 men aged 18 to 49 applied 5% solution (n = 157), 2% solution (n = 158) or placebo (n = 78) twice daily [1]. The 5% solution was significantly better than both 2% and placebo on nonvellus hair count and on patient and investigator ratings of scalp coverage, and itching and local irritation were more frequent with 5% [1].

In the matching trial, 381 women aged 18 to 49 used 5% solution (n = 153), 2% solution (n = 154) or placebo (n = 74) twice daily for 48 weeks [2]. The 5% solution beat placebo on all three primary measures and beat 2% on patient-rated treatment benefit, and the 5% group had more itching, more local irritation and more excess hair growth (hypertrichosis) than the 2% group or placebo [2].

A 2018 network meta-analysis of non-surgical hair loss treatments counted 45 drug-related adverse events reported for minoxidil 5% and 23 for minoxidil 2%, more than any other treatment it compared [8]. Those are event counts pooled across the studies it included, not incidence rates.

Foam versus solution

113 women with androgenetic alopecia were randomized to 5% minoxidil foam once daily or 2% solution twice daily for 24 weeks [5]. The foam was noninferior for nonvellus hair count and hair width, and women using foam had significantly lower rates of local intolerance (P = .046), especially itching and dandruff [5]. The comparison there was foam against the 2% solution, not against the 5% solution.

In men, a 16-week double-blind trial of 352 men found that 5% foam increased hair counts compared with placebo, and 143 of them continued into a 52-week open-label phase in which the foam was well tolerated [9]. The foam vehicle is propylene glycol-free [9], whereas the 2% solution used as the comparator in the women's foam trial contains propylene glycol [5].

Hypertrichosis and unwanted facial hair

In the 48-week women's trial, hypertrichosis was more common with the 5% solution than with the 2% solution or placebo [2]. Both the men's and women's OTC labels list unwanted facial hair growth among the events they flag [3][4].

How much minoxidil gets into the blood

A review estimates that approximately 1.4% of topical minoxidil is absorbed through the skin [6]. In a separate study, 12 adult men applied radiolabeled 1% and 5% solutions to a bald scalp area nine times, with the radioactive dose on days 1 and 9: 1.6% to 3.9% of the applied radioactivity was recovered in urine, none in feces, and 41% to 45% was recovered from the skin surface and scalp and pillowcase washes [7]. The authors estimated that treating the whole scalp would deliver roughly 2.4 to 5.4 mg/day systemically, and none of the 12 men had an adverse reaction during the study [7].

The men's 5% Drug Facts label flags heart disease; it also lists chest pain, rapid heartbeat, faintness or dizziness, sudden unexplained weight gain, and swelling of the hands or feet among its stop-use events [3].

The FDA's adverse event database holds reports on minoxidil, but the agency states that rates of occurrence cannot be established from those reports, that reports may be duplicated or incomplete, and that a report does not establish that the drug caused the event [10].

Hair texture and colour

The label notes that some people have experienced changes in hair color and/or texture [3].

Pregnancy, children and accidental exposure

The label is for external use only, states that the product may be harmful if used when pregnant or breast-feeding, and states that it should not be used by anyone under 18 [3]. It says to avoid contact with the eyes and, if contact happens, to rinse with large amounts of cool tap water [3]. The women's foam label adds that the product is extremely flammable and that fire, flame and smoking should be avoided during and immediately after application [4].

In January 2026 the FDA approved label additions for the Rogaine products telling users to keep the product out of reach of pets and to avoid contact between children and minoxidil application sites [12].