When you drink caffeine (adenosine antagonist) you can build up a tolerance. This is caused by an increase in adenosine receptors in the brain. When you stop drinking caffeine, the added adenosine receptors have no antagonists and thus it leads to headaches and such caused by increased blood flow. I imagine the adenosine receptors around the hair follicle would try to do something similar and need more caffeine to shut these receptor down. My question is how high can the number of these receptors go? Since it takes roughly a week to withdrawal off of caffeine I imagine there is an upper limit that isn't very high. I don't think the hair follicles could increase adenosine receptors high enough to undercut the effects of caffeine at substansial doses, but I could be wrong.

Also, would it be good to exploit this situation of increased receptors by applying minox or some adenosine agonist for the week or so that it takes for the caffeine tolerance/increased receptors to dissipate? Would this help, or would it screw up the independent pathways by which these chemicals work? Would an agonist one day and antagonist another day be feasible/smart? It would seem wise to stimulate the follicles with whatever stimulation one could give it, but mixing agonists/antagonists seems weary to me.

A lot of questions, in search of answers. Anyone can chime in.

Great questions....but I'd be surprised if anyone really knows the answers to them. Well I'm sure there is someone out there who probably has a good idea...but here? Hmmmmm

It's a pretty advanced topic and I can't really answer.  What I can say is that not everything builds a tolerance over time in the body - some things do, some things don't.  It also may be very individualistic what rate that occurs at.  There are definitely people who have been taking things like minoxidil or propecia who have not gotten tolerance to them or whom it has taken over a decade for it to happen to.

There's also an additional factor to consider besides tolerance, and that is that as you age, both your hormone levels and reactions to those hormones change.  Men produce lower levels of hormones as they age, but their bodies also may become more sensitive to them.  So what some perceive as tolerance can also be simply the body changing it's own hormones and bodily reactions separate from the medicine.

If you want to increase absorption, a damp head.  Depends on what best means - best for what - how your hair will look, or best for skin absorption?

Absorption should be best after you've showered/shampooed and gotten the excess water off.  I don't think just putting your head under water for a few seconds and towelling off would have the same effect.  Also if the hair is dry what hair is there may absorb some of the liquid instead of it getting absorbed into the skin.