I recently tried larger-than-normal methylfolate supplements. I had known that my genes caused problems with processing folate (MTHFR T/T), but hadn’t noticed any effects from supplementing at 800mcg/day.
Due to a report that several milligrams/day helped with depression, I changed from 400mcg/day to 2mg/day. I felt like my mind started working better within hours (although I haven’t seen much change in behavior). I saw a clear and large improvement in my heart rate variability starting after one day.
I’ve experimented for 5 weeks randomly altering my dose from 1 to 3 mg/day. On the week when I switched from 3 to 1 mg, my mood slowly got worse. I felt much better withing hours of switching back to 3 mg. I haven’t noticed any clear difference between 2 and 3mg.