Not very.
Since a search will yield you the normal schpiel, I'll put it to you this way:
Have you ever used caffeine to stay awake (coffee, energy drinks, etc)?
Over time if you use coffee every morning, you actually get to the point where you can't become alert until you have drank the coffee, a stimulant. Minoxidil, a hair stimulant, is very much the same (not in how it works, but by the fact that it stimulates something..)
If you stop drinking coffee, you will stop being awake in the morning for a long time. You may even develop "withdrawal" symptoms in which you feel so sluggish that you are borderline depressed and may find it difficult to be alert to any reasonable degree.
How does this translate to minoxidil?
If you quit minoxidil, you will stop stimulating the follicle to grow. The hair follicle, which relied on minoxidil for its growth stimulation, has "forgotten" how to grow hair on its own. As a result, the hair follicle theoretically may stop growing hair and/or may go into dormancy or even die. Studies show that after minoxidil discontinuation you will shed an enormous amount of gained hair to the point where you will be worse off than if you'd never used minoxidil. After a period of time ( a few months, I think) the level returns to baseline (the level at which you would be had you NEVER applied minoxidil).
The bottom line, however, is that you will be miserable for a few months while your hair adjusts to the loss of its stimulation. The follicles have to regain endogenous hair stimulation, which takes time. Depending on how long you've used minoxidil, your "baseline" may be considerably less than your current head of hair if minoxidil worked for you.
My suggestion:
If you are going to quit minoxidil, do so VERY slowly. I considered doing it as well, but I am honestly too frightened to weather the shed and then pray that it all grows back using finasteride.
My suggestion for quitting minoxidil (UNTESTED!):
For the first month, simply use minoxidil once per day. Most people notice a negligible loss of gained hair when they reduce the dosage to once daily.
After 30 days, try applying minoxidil every other day. Try to apply it at the same time every other day. Consistency is important.
After another month, try to apply minoxidil every third day.
In the final month, apply minoxidil once per week.
This was just an example of what might work. It is likely that nothing will allow you to avoid shedding your gained hairs even if you are on finasteride treatment. However, by tapering your dose it is likely that you will lessen the withdrawal "shock" to your hair follicles.
BOTTOM LINE: IF YOU TRY THIS or any other variation of quitting, PLEASE COME BACK AND LET US KNOW HOW IT TURNED OUT. THIS IS A FREQUENT QUESTION AROUND HERE.
