FUE hair transplant 6 months post op. Now my density is not good enough. Can Minoxidil get more density or not?

It can take 6 to 12 months after surgery to see results.  If you are concerned it is best to contact your doctor.

If you are not using a Laser Cap from day 10 of your procedure, I would wait until month 12 and then revisit with your doctor to review results.
With the use of a Laser Cap and SmartGraft, we are seeing outstanding thick results at 5 months. Without, it can take up to 12 months to see the true result.

It takes 8-12 months to see your final results from a hair transplant.  Give it at least another two months, then go see your surgeon to review preop photos and discuss results and concerns.  Minoxidil can help increase the density of your native hair, but it stops working when you stop using it.

Being six months out from your hair transplantation, you have not reached a maximal growth level.  It is too early to proclaim that it failed.  I am very hopeful that over the next couple of mother, that you will start to see much thicker hair and density, since final growth can take even as long as 15 months following the procedure.  Minoxidil is a good choice to thicken the hair at this time and you should consider other treatments such as PRP and Finasteride therapies.

At 6 months you should see reasonable growth, but not final density.  Laser and Rogaine can help but adequate density should occur on it's own. I generally see my patients at 6 months to see where we are.  A year is a long time to wait for results and it can be frustrating.  I like to alleviate that anxiety by examining them and reassuring them they have 6 months to go.

I would wait another two months and if by that time you are not happy with the results, see your surgeon and if your surgeon is a caring doctor, he will make things right with you