A 400 mcg folate supplement is rather a low dose. You could start taking two a day to see if that helps.
If you go to Amazon or Ebay or any other website selling supplements and search for methylfolate you should find supplements available with doses of 800mcg per tablet or 1000mcg per tablet. There may be higher doses available than that but I've never taken anything higher than 1000mcg per day. I don't know how tolerable they would be.
3 weeks is probably a little early to be retesting, I usually suggest 3-4 months. That sid I agree with humanbean and 400mcgs is a fairly lowish dose. It will work for some but those with MTHFR genes, which are common, will need somewhere up to 1,000mcgs a day.
You can just top up the B complex you're taking by buying a separate 400mcg methylfolate and add that in slowly until you work out how much you need.
I have MTHFR genes and didn;t feel any benefit at all from the 400mcgs in a B complex. It wasn't until I switched to a 1,000mcg capsule before a blood test that I felt the difference.
Jarrows offer a 400mcg methylfolate but there are a number of relatively cheap brands available that work.
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