How Minoxidil Works: The Complete Science

The accidental discovery, the four mechanisms of action, and why it doesn't work for everyone.

Updated March 2026  •  Medically reviewed by [REVIEWER NAME, CREDENTIALS]

Minoxidil is the most widely used hair loss treatment in the world. Over-the-counter topical formulations have been available since the late 1980s, low-dose oral prescriptions are surging, and yet most people using it couldn't explain why it works. Many websites can't either — they stop at "increases blood flow to the scalp," which is only one piece of a more interesting story.

Here's the full picture: how minoxidil was discovered, what it actually does to your hair follicles, and why roughly 40–50% of topical users don't respond — a problem that has a solution.

The Accidental Discovery

Minoxidil was never designed for hair loss. In the 1970s, Upjohn Company developed it as an oral medication for severe hypertension (high blood pressure), marketed under the brand name Loniten at doses of 10–40 mg per day.

Almost immediately, clinicians noticed something unexpected: patients on Loniten were growing hair — everywhere. Face, arms, back, legs. This unwanted side effect, called hypertrichosis, was a problem for blood pressure patients. But for researchers, it was a clue that minoxidil was doing something powerful to hair follicles.

Upjohn pivoted. They developed a topical formulation that could be applied directly to the scalp, concentrating the drug where it was wanted. In 1988, topical minoxidil (brand name Rogaine) became the first FDA-approved treatment for hair loss. It remains one of only two drugs with FDA approval for androgenetic alopecia — the other being finasteride.

The Four Mechanisms of Action

Minoxidil doesn't work through a single pathway. It stimulates hair growth through at least four distinct mechanisms:

The Prodrug Problem: Why It Doesn't Work for Everyone

Here's the part most articles skip, and it explains the most frustrating aspect of minoxidil treatment: the ~40–50% non-response rate with topical.

Topical minoxidil is a prodrug. The minoxidil you apply to your scalp is not the active form. It needs to be converted into minoxidil sulfate by an enzyme in your scalp called sulfotransferase (SULT1A1). Only the sulfated form actually stimulates hair follicles.

The problem: SULT1A1 activity varies enormously between individuals. Some people have high enzyme activity and convert topical minoxidil efficiently. Others have low activity and can't convert enough of the drug to produce meaningful results — no matter how consistently they apply it.

This is why two people can use the exact same topical minoxidil product with the exact same consistency and get completely different results. It's not about the product or the technique — it's about their scalp biochemistry.

The Oral Minoxidil Solution

This is where oral minoxidil changes the game. When taken orally, minoxidil is converted to its active sulfate form by the liver — bypassing the scalp enzyme entirely. A 2024 study (Jimenez-Cauhe, Wiley) found that patients with low follicular SULT1A1 responded better to oral minoxidil than patients with high activity — 85% improvement vs. 42.9% (p=0.009).

In other words: if topical minoxidil didn't work for you, oral minoxidil might work better than it does for people who responded to topical. The enzyme that was your bottleneck becomes irrelevant.

For a deep dive into non-response and what to do about it, see our Minoxidil Non-Responders Guide.

Can You Test for SULT1A1?

Yes. The Daniel Alain Minoxidil Response Test (MRT) analyzes 6 hair strands for SULT1A1 activity, claiming 95.9% accuracy for predicting topical response. It costs about $150. Research has also shown that topical tretinoin and microneedling can boost SULT1A1 activity in some non-responders. Full details: The Minoxidil Response Test.

What Minoxidil Can (and Can't) Treat

Effective for:

• Androgenetic alopecia (genetic pattern hair loss) — the primary FDA-approved use
• Telogen effluvium (stress/weight-loss shedding) — a 2025 Japanese trial showed 70% improvement
• Beard growth (off-label, significant anecdotal and emerging clinical evidence)
• Alopecia areata (as adjunct therapy)

Less effective for:

• Complete baldness (follicles that have been dormant for years may not reactivate)
• Scarring alopecia (where follicles are permanently destroyed)
• Frontal hairline recession (works better on the crown; DHT blockers are more important for temples)

Ready to Start?

If you're considering minoxidil, you can pick up topical formulations (foam or liquid) on Amazon without a prescription — Kirkland 5% is the best value at ~$8–12/month.

If you want to explore oral minoxidil or custom compounded formulations, you'll need a consultation. Sesame Care offers same-day telehealth appointments starting at $44.