It's also very irresponsible of the physician.
Systemic absorption of minoxidil was previously used as a treatment for hypertension (high blood pressure). It is a fairly potent vasodilator. By dilating the peripheral capillary beds, you can decrease the mean arterial blood pressure and treat high blood pressure. If you want an explanation of how HTN is damaging, I could go into that but it's not really important for this discussion, I digress. :stfu:
If you can picture a balloon full of water hooked up to a hose it might be a helpful illustration.
There are three ways that you can decrease the pressure exerted on the balloon's inner surface.
1. Let water out of the balloon. Because the circulatory system is a closed system macroscopically, the only way to let volume out of it would be to BLEED a person. We don't do that for obvious reasons.
2. Let water out of the balloon by increasing urine output. This is easily accomplished by a heavy night of drinking (inhibits ADH/vasopressin excretion). But seriously, diuretics do the trick nicely.
3. Increase the overall size of the balloon, this will decrease the FORCE per SURFACE AREA, because you will have a constant amount of force exerted but it will be spread out across a greater distance.
Minoxidil when taken orally does (3) by dilating the vasculature.
Its positive effects for hairloss were discovered by accident. An "adverse reaction" of minoxidil usage was found to be hirsuitism, or the unexpected and relatively uncontrolled growth of hair. In an effort to harness this previously-unwanted side effect, someone had the bright idea to make it bioavailable directly on the scalp. This prevents systemic absorption and therefore peripheral vasodilation in unwanted places.
I would only use minoxidil topically. It's naive to think that you won't be causing systemic effects that aren't necessary and potentially dangerous.
I am only a medical student and not a fully-boarded dermatologist, but I have looked into this a lot. Actually, if I had it to do over again I wouldn't use minoxidil. It's a pain in the ***.