When you say hairfall control remedies, are you speaking about herbal and nutritional supplements? I haven't seen any specific correlation with supplements for BPH and high blood pressure also being used to treat hair loss, but I would definitely agree that anything that vasodilates and boosts circulation in general would potentially increase scalp circulation, as well.I think the reasoning for Arnica, is that it stimulates blood flow and also acts as a vasodilator. Perhaps this causes more blood to reach the follicles ?
Since you are studying (Homeopathic) medicine, maybe you could comment on this. I am noticing some patterns in hairfall control remedies. Remedies originally meant for blood pressure, as well as those meant for BPH seem to help control hairloss. Do you also notice this pattern?