If minoxidil is applied right after dermarolling, then it isn't impressive at all.
I did minoxidil and dermarolling for more than 6 months and had 0 gains. I never used minoxidil faster than 24 hours before demarolling.
If you use it soon after injury minoxidil will go systemic. Will it promote more hair growth? Yes, probably, but so will drinking or injecting it. That is to be expected, that is how they found it.
But the problem is - side effects, mainly like blood pressure changes, water retention and possible heart attack.
The results needling + minoxidil in my opinion cant be explained by the minoxidil going systemic; it has a half life of say 12 hours so giving you at best one full day of effective systemic exposure. Then applying right after needling would give someone needling at a once per 2 week frequency (per the studies) too little exposure for very good results. My guess is that some synergy is in fact occuring.
That being said, I have needled without minoxidl for about 4 months without obvious result or deteriation (even with all my pictures I find it hard to judge if anything has changed), I dont know if I have maintained I think one would need a trichogram for that. I now added nanoxidil for one month + needling (supposed to resemble molecular structure of minoxidil but I have my doubts still).