How does minoxidil work?

How Minoxidil Works

Minoxidil stimulates hair growth primarily by shortening the telogen (resting) phase and forcing hair follicles into premature anagen (growth) phase, while also prolonging anagen duration and increasing follicle size, though its precise molecular mechanism remains incompletely understood. 1, 2

Primary Mechanisms of Action

Hair Cycle Modulation

• Minoxidil shortens telogen phase, causing resting hair follicles to prematurely enter the active growth (anagen) phase 2, 3
• Prolongs anagen phase duration, allowing hair to grow for longer periods before entering the resting phase 2
• Increases hair follicle size, resulting in thicker, more robust hair shafts 2, 3
• This synchronization of the hair cycle explains the initial increased shedding some patients experience when starting treatment—old telogen hairs are pushed out as new anagen hairs begin growing 1

Vascular and Cellular Effects

• Minoxidil acts as a potassium channel opener, causing hyperpolarization of cell membranes, though clear demonstration of KATP channels in hair follicles has been elusive 1, 2
• Functions as a vasodilator, potentially widening blood vessels to deliver more oxygen, blood, and nutrients to follicles 1
• The active metabolite minoxidil sulfate (created by sulfotransferase enzymes in the scalp) appears responsible for the hair growth effects, similar to how it works systemically for blood pressure reduction 2

Additional Cellular Actions (In Vitro)

• Stimulates cell proliferation in various skin and hair follicle cell types 2
• Inhibits collagen synthesis in cultured cells 2
• Stimulates vascular endothelial growth factor (VEGF) and prostaglandin synthesis, though the clinical relevance of these in vitro findings to actual hair follicle biology remains uncertain 2

Clinical Efficacy Evidence

Demonstrated Effectiveness

• Both 5% and 2% topical minoxidil solutions are superior to placebo for increasing nonvellus hair count and improving hair growth/scalp coverage in female pattern hair loss 4
• 5% minoxidil demonstrates superiority over 2% formulation in patient-assessed treatment benefit 4
• Measurable changes disappear within months after discontinuation, requiring continuous application once or twice daily to maintain hair gained 1

Combination Therapy

• PRP combined with topical minoxidil is more effective than either treatment alone for androgenetic alopecia, though minoxidil monotherapy remains effective 5
• Minoxidil is better tolerated than PRP injections due to pain associated with injections 5

Important Clinical Considerations

Common Pitfalls

• Initial increased shedding is expected and normal—this represents synchronization of the hair cycle as telogen hairs are replaced by new anagen hairs 1
• Continuous application is mandatory—benefits cease within months of discontinuation 1
• Individual response varies based on genetic factors and sulfotransferase enzyme activity in the scalp 5

Side Effects

• Local irritation and allergic contact dermatitis are the most common adverse reactions, sometimes due to propylene glycol in formulations rather than minoxidil itself 1
• Hypertrichosis (unwanted facial hair growth) affects approximately 15% of patients on low-dose oral minoxidil 6
• Increased occurrence of pruritus and local irritation with 5% versus 2% formulations 4

Formulation Considerations

• Modern low-propylene glycol formulations offer better cosmetic acceptance and dermatological safety 3
• 5% foam formulation provides once-daily dosing option with demonstrated efficacy 7