The biology of pattern hair loss
Androgenetic alopecia — male and female pattern hair loss — is the most common form of hair loss. It is driven primarily by sensitivity of hair follicles to dihydrotestosterone (DHT), a more potent metabolite of testosterone converted by the enzyme 5-alpha reductase.
In genetically susceptible follicles, DHT exposure progressively shortens the hair growth phase and miniaturizes the follicle itself. Over time, terminal hairs become vellus (fine, short) and eventually the follicle ceases producing hair entirely. The shrinkage is gradual — which is why early intervention preserves more hair than late intervention.
The first-line treatments with the strongest evidence
Two interventions have decades of randomized controlled trial support:
- Finasteride 1mg/day — inhibits type II 5-alpha reductase, reducing DHT by ~70%. The original 5-year trial showed 48% of men had visible regrowth and an additional 42% maintained their hair, vs. progressive loss in the placebo group.[1]
- Topical minoxidil 5% — vasodilator that extends the anagen (growth) phase. Effective in both men and women.[2]
- Dutasteride 0.5mg/day — inhibits both type I and type II 5-alpha reductase, reducing DHT ~90%. Marginally more effective than finasteride in head-to-head trials.[3]
What about oral minoxidil?
Low-dose oral minoxidil (1.25–5mg) has gained increasing evidence and use. A 2020 systematic review found oral minoxidil to be effective for both male and female pattern hair loss with manageable side effects when properly screened and dosed.[4]
For some patients, compounded combinations (oral minoxidil + finasteride, sometimes topical at compounded strengths) offer convenient single-daily-dose adherence — a meaningful factor in a treatment that requires consistency over years.
Why baseline labs matter
Hair loss is often pattern hair loss, but not always. A responsible evaluation rules out contributing or alternative causes: iron deficiency (low ferritin), thyroid dysfunction (TSH, free T3, free T4), vitamin D deficiency, autoimmune patterns (alopecia areata), or hormonal issues in women (PCOS, androgen excess).
Treating pattern hair loss without checking these foundations means missing easily addressable contributors. A simple set of labs — CBC, ferritin, thyroid panel, vitamin D, and in women, a hormone panel — clarifies the clinical picture and is part of any thoughtful evaluation.
What to do with this information
If you are noticing pattern hair loss, time is on the side of acting sooner. Miniaturized follicles can often be restored to terminal hair production; dead follicles cannot be revived. A clinician who can confirm the pattern, rule out contributing factors with appropriate labs, and prescribe an evidence-based protocol is the right first step.
