Toppik with Minoxidil, is it safe or not?

In  my opinion, The biggest issue with Toppik and minoxidil is the potential decreased absorption of the minoxidil. Many physicians believe that the minoxidil will still penetrate the fibers. There are no studies regarding the possible negative effects of minoxidil solution carrying pigment or fibers into the scalp.
Jeff Rapaport MD FAAD
Realself Verified All-star

It is not dangerous in the manner you have described as these particles don’t get into the scalp like this (as they are too big). But having Toppik on top can limit the ability of the minoxidil to get in. Ideally, the Toppik is washed off before applying minoxidil. 

Excellent question. I have hundreds of patients applying Minoxidil and hair fibers. I always recommend if it is possible: wash and dry the scalp first then apply Minoxidil and few minutes later apply Toppik. The experience with my patients applying hair fibers first then Minoxidil is not good related to less Minoxidil absorption and decrease of the results in the short and long term. Good luck.