Minoxidil was originally developed as an oral antihypertensive agent. Its effect on hair growth was observed as a side effect, leading to the development of topical formulations that became the first pharmacological treatment approved for androgenetic alopecia. Decades of clinical use have established its safety and efficacy profile, and the emergence of low-dose oral minoxidil has broadened its applicability significantly.
Minoxidil works differently from 5-alpha reductase inhibitors — it promotes hair growth rather than preventing hair loss, making it a complementary rather than competing therapy.
Mechanism of action
Minoxidil is a potassium channel opener and vasodilator. Applied to the scalp, it increases blood flow to hair follicles and is thought to directly stimulate follicle keratinocytes to extend the anagen (growth) phase of the hair cycle. It also appears to upregulate vascular endothelial growth factor (VEGF), promoting the perifollicular vasculature on which healthy follicles depend.
Importantly, minoxidil does not affect DHT — it works orthogonally to 5-alpha reductase inhibitors, making the combination of minoxidil and dutasteride (or finasteride) a logical and well-supported pairing.
Topical vs oral minoxidil
Topical minoxidil (2% or 5% solution or foam) is applied directly to the scalp once or twice daily. It is effective, but compliance can be an issue — the application is time-consuming and can leave the scalp feeling greasy. Some patients also develop contact dermatitis to the propylene glycol carrier used in some formulations.
Low-dose oral minoxidil (typically 0.625–2.5mg daily in women; 2.5–5mg in men) has demonstrated comparable or superior efficacy to topical formulations in recent trials, with a simpler daily regimen and avoidance of scalp application issues. It is used off-label and requires a medical assessment for suitability — particularly regarding cardiovascular history and baseline blood pressure.
Dr Kynan's recommendation is generally for the oral approach. Topical minoxidil is a prodrug — it only works once it is converted to its active form, minoxidil sulfate, by the enzyme sulfotransferase (SULT1A1) in the hair follicle itself. Follicular SULT1A1 activity varies significantly between individuals, and published estimates suggest that roughly 30–40% of people have low enough follicular enzyme activity to respond poorly — or not at all — to topical minoxidil, regardless of how consistently it is applied.* Oral minoxidil bypasses this bottleneck entirely, since it is absorbed systemically and converted to its active form in the liver rather than at the follicle. For this reason, oral minoxidil is a more reliable starting point for most patients, rather than risking months of topical use before discovering a poor genetic response.
Treatment details
Formulations
Oral preferred
Topical remains available, but oral is generally recommended first-line to avoid genetic non-response at the follicle. Final choice is discussed at consultation.
Onset
3–6 months
Initial shedding is common in the first 4–8 weeks as telogen hairs are displaced by new anagen growth. This is expected and not a sign of treatment failure.
Commitment
Ongoing
Cessation results in loss of treatment benefit within 3–6 months. Minoxidil is a maintenance therapy, not a cure.
Side effects
Topical minoxidil is generally well tolerated. Scalp irritation and contact dermatitis can occur, particularly with propylene glycol-containing formulations. Unwanted facial hair growth has been reported, particularly in women using higher-strength topical preparations.
Oral minoxidil side effects include fluid retention, palpitations, and — dose-dependently — hypertrichosis (increased body hair). These are dose-related and managed by starting at the lowest effective dose. Oral minoxidil is contraindicated in patients with certain cardiovascular conditions; a baseline history and blood pressure measurement are taken at consultation.
References
- * Goren A, Castano JA, McCoy J, Bermudez F, Lotti T. Novel enzymatic assay predicts minoxidil response in the treatment of androgenetic alopecia. Dermatol Ther. 2014;27(6):171–173. doi:10.1111/dth.12111