Thats exactly the dosage Im taking, but I have an appointment soon and Im going to ask if I can try that other one, thats 180 mg but it gives is more slowly. So that would be 6x 90 + 180 mg a day.

I had no idea this is considered a high dose?

Anyway, as far as I know, there is no problem in taking a high dose of mestinon on long term. I know a woman who takes over 800 mg everyday, for over 30 (maybe even 40 or longer) years now. And it still works the same for her, no problems whatsoever.