We dermaroll to create collagen, applying Minoxidil into open wounds created by dermarolling negates the collagen production that we are trying to create. Also you may be causing the Minoxidil to go systemic (into your wider body) and that can cause side effects.
We have been recommending to not apply Minoxidil for at least 24 hours after dermarolling with .5 mm.
If you use a longer dermaroller than .5 mm, wait longer. With a 1 mm dermaroller, we’d recommend waiting at least 2 days before applying Minoxidil.