Doc,
I read that Rogaine has a half-life of about 22 hours in skin. Assuming you have no side effects from applying it all at once, could you apply double the recommended amount once per day and have the same effect?
Minoxidil was originally a not-that-great oral high blood pressure medication called Loniten. The results varied in the treatment of high blood pressure and eventually the medication was turned into a topical after the hair growth side effect was noticed. The drug stays in the plasma for about a 4 hour half life, but on the skin it stays much longer with slow absorption suggesting that once a day application may be satisfactory.
I can not comment on the official use of twice a day application to the scalp, but clearly more of it will be used and sold with twice a day applications. If you double the dose and apply it once a day, the drop in blood pressure side effect becomes more prevalent.
