Will my hair fall out when I stop using Minoxidil?

The  response of beard hair to minoxidil is different than that of the scalp. Minoxidil can take small, thin, wispy vellus beard hairs and convert them into thick terminal hairs. This process usually takes between 6 and 12 months. Once the terminal  beard hairs are growing, discontinuation of the minoxidil should not affect these terminal beard hairs.PRP hair md.com

Minoxidil is a FDA approved hair loss medicine. It requires long term use in order to give good results. When quit the hair thats been gained because of minoxidil can shed. 

It really depends on a number of factors - especially your current age. Beard growth does not reach a maximum until age 30 so any use before age 30 is more likely to simplify help the process by which vellus hairs become terminal hairs. However even then there is a small chance some hairs will fall out if minoxidil is stopped. That risk is low. If one is using minoxidil for other situations it is possible that hairs are solely dependent on minoxidil. Please see your physician if concerned.