How do the mechanisms of minoxidil and finasteride differ in promoting hair growth?

• A. Minoxidil inhibits 5-alpha-reductase; finasteride opens potassium channels.
• B. Minoxidil opens potassium channels to promote growth; finasteride inhibits 5-alpha-reductase.
• C. Both act by increasing estrogen levels.
• D. Both directly stimulate hair follicle immune response.

Answer: (B)

Mechanisms differ: minoxidil promotes hair growth by opening potassium channels in the hair follicle and surrounding vessels, which causes vasodilation and increased blood flow to the follicles, helping prolong the growth phase of the hair cycle. Finasteride promotes growth by inhibiting 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT); with less DHT in the scalp, androgen-driven miniaturization of hair follicles decreases, allowing hairs to regrow thicker and longer.

The idea that minoxidil inhibits 5-alpha-reductase or that finasteride opens potassium channels isn’t accurate. Estrogen increases or direct stimulation of the hair follicle immune response aren’t the mechanisms at play for these drugs.