Hair Glossary

Minoxidil, sold under the brand name Rogaine, among others, is a medication used to treat high blood pressure and pattern hair loss.  It is an antihypertensive vasodilator.
It is available as a generic medication by prescription in oral tablet form and over-the-counter (OTC) as a topical liquid or foam

Minoxidil Was Originally Designed For Treating Hypertension

Oral minoxidil, when used for hypertension, is generally reserved for use in severe hypertension patients who can not respond to at least two agents and a diuretic. Minoxidil is also generally administered with a loop diuretic to prevent sodium and potassium retention.

It may cause reflex tachycardia and thus is often prescribed with a beta blocker. 
Topical Minoxidil

Minoxidil applied topically, is widely used for the treatment of hair loss. It is effective in helping promote hair growth in people with androgenic alopecia (AGA) regardless of sex (MPHL or FPHL). 

Minoxidil must be used indefinitely for the continued support of existing hair follicles and the maintenance of any experienced hair regrowth.

Low-dose oral minoxidil is used off-label against hair loss.  Its effect in people with alopecia areata is unclear, although some people experience measurable results.

The association of oral minoxidil with Janus Kinase inhibitors (JAK inhibitors) termed oral adjuvant minoxidil, seems to increase hair regrowth in patients refractory to JAK inhibitor monotherapy

Effectiveness Of Minoxidil

Minoxidil is less effective when the area of hair loss is large. In addition, its effectiveness has largely been demonstrated in younger men who have experienced hair loss for less than 5 years

Minoxidil use is indicated for central or vertex hair loss only. Two clinical studies are being conducted in the US for a medical device that may allow patients to determine if they are likely to benefit from minoxidil therapy.