Deplin [0] is a patented prescription version of Vitamin B-9 aka L-Methylfolate. It's approved as an add-on treatment for when so-called antidepressants don't help with a person's symptoms. There's a genetic test that tells if a person is a poor methylator who especially needs Folate instead of folic acid.

I don't know how they decided to run the genetic test, I just heard that they did and that folate really helps her. She eventually switched to non-prescription folate (from the supplement aisle), probably mostly because of cost, or maybe some other reason.

Folate is cheap enough to experiment with: if you notice something dramatic, keep taking it.

[0] https://deplin.com/what-is-deplin