Re: Why would Rogaine give chest pains?

Hello Eric!  Thank you for your question.

You asked:  "Why would Rogaine give chest pains?  It's listed as one of the 
rare side effects... I'm curious as to why in the world a topical solution 
would give someone chest pains?  What are the interactions of the chemicals 
which cause sensations of pain in a different part of the body?  Is it 
serious or damaging?"

***The following information is not presented as medical advice by MadSci 
or G. Monreal and should not be taken as such.  All the information 
summarized and explained below can be found in further detail on the 
following excellent websites:
www.regroe.com/works.html
www.rxmed.com/monographs2/minoxi.html 


Rogaine contains the ingredient minoxidil, which is a vasodilator.  A 
vasodilator works to lower blood pressures by relaxing the peripheral 
vessels and increasing perfusion of the tissues.  This relaxation decreases 
the resistance inside the vessels and creates an overall decrease in 
systemic blood pressures.  If the pressures drop too much, the body will 
compensate by increasing the heart rate in an effort to maintain 
appropriate circulation, and the body may also retain fluids in an effort 
to add more volume to the circulation (which increases pressures).   

Vasodilator --> Relaxation of the peripheral blood vessels --> Decrease in 
systemic blood pressure -------- if pressures drop too much, then:   Low 
pressures --> Increased Heart Rate and Retention of Fluids --> Blood 
pressures come back up

Vasodilators are used to help lower blood pressures in people who have high 
blood pressures (hypertension) by reducing the afterload on the heart, so 
the heart doesn't have to work as hard to pump the blood through the body. 
OK, how do they help?

Here's an analogy:
     Imagine taking a mouthful of water and trying to blow that set volume 
through a coffee stirrer in a fixed amount of time.  The coffee stirrer is 
very, very narrow (has high resistance), and you will have to work very 
hard to blow all the water through in enough time.  The pressures inside 
that straw as the water pushes through will be very great, and you will be 
tired afterwards (you are the heart).  This situation is comparable to 
someone with high blood pressures.
     Now, imagine that you have to blow the same amount of water in the 
same amount of time through a regular drinking straw.  The straw is wider 
(like a dilated vessel), and the resistance inside is lower, so you will 
not have to work so hard to push that water through, nor will you be as 
tired afterwards (you, as the heart, will appreciate not being as tired!). 
 

Now, what does all this have to do with minoxidil??

Back in the early 1980's, minoxidil came onto the market as a drug for 
lowering high blood pressures.  Scientists and doctors theorized that since 
it is a vasodilator, it should dilate the blood vessels in the scalp, 
perfusing the scalp tissue with oxygen-rich blood and nutrients in hopes of 
stimulating the growth of new hair follicles and encouraging cell division 
of the hair matrix cells, producing thicker strands. 

So why is one of the extremely rare side effects of minoxidil chest pains?

If someone is already taking antihypertensive medication for high blood 
pressure and decides to use minoxidil, in theory the addition of this 
second pressure-lowering agent could drop the blood pressures lower than 
they need to be.  Likewise, someone in congestive heart failure may already 
have low pressures to begin with.  Their heart is already beating faster, 
and the body is already retaining fluids in an effort to maintain 
pressures.  Adding a vasodilator to that mix could, in theory, make the 
situation worse by lowering pressures even further (and thus encouraging 
the heart to beat even faster and the body to retain even more fluids).  
How do chest pains develop from all this?  When pressures get too low for 
whatever reason, and the heart is unable to perfuse it's own coronary 
vessels adequately, regions of the heart can become ischemic as the oxygen 
supply to that area is reduced.  The heart then switches from aerobic to 
anaerobic respiration, and toxic by-products accumulate (such as lactic 
acid), leading to fatigued heart muscles and chest pains.

Hope this information helps to answer your questions!

Sincerely, 
G. Monreal