I quit Regaine and am back to shedding. Will it work again?

Minoxidil (Rogaine) will only work when you use it.  You will lose the hairs gained when you stop using it.  Once you restart the medication you may not regain the hair that was lost.

If the minoxidil worked for you before, there is every chance it will work again. However you may not regain the hair you have lost, only stabilise what you have. It does take 6-9 months of regular usage to know if it is working so I suggest you stick with it. if you are really worried about your hair loss you might want to consider taking Propecia

If you have genetic MPHL your hair loss is progressive, To regain your hair back the best option is hair transplants, you can use rogaine to slow down the furture hair loss.Usually any kind of medical regiment is used to slow down future hair loss and in process you may gain some hair back.  If you decide to change or discontinue the product you need to taper it off and not to abruptly stop using it. 

If you stop the drug minoxidil (Rogaine), you will lose the minoxidil dependent hairs. You must always remember that genetic hair loss in men is a progressive process. I see changes in people who are on finasteride or minoxidil that indicate that over time the drug is less effective of they report that they stopped it and saw hair loss fairly quickly. My best advice to you is restart the minoxidil, expect that the benefit will return and stay the course.