Here is an update:
I had been on 18 mg of folinic acid for a little over 9 months, which is the dose that seems to agree best with me. I have also been on a dairy-free diet for about 5 years, but in the past year I have scrutinized labels even more to make sure I don't get any milk products, not even milk fat (believe it or not, some 70% cocoa dark chocolate have milk-fat as ingredients, so watch out).
I've had ups and downs, but the main take away is that I have been completely off SSRIs for 9 months, and I have been able to exercise on a regular basis. I have not had irrestible sleepiness in the afternoons anymore, neither have I felt very heavy and very cold. So this is working for me long-term.
HOWEVER, something happened in the past two months, that could be a side effect of long-term use of leucovorin, though it could also just be a coincidence unrelated to leucovorin:
Two months ago I suddenly started having intense burning and tingling on my tongue, gums, palate and throat, as well as around my lips, as if I had just eating chili peppers or burned my mouth. Strangely, I couldn't see anything, no obvious redness, inflamation or sores. On and off, my lips would dry off and my mouth would feel very dry too. I went to my family doctor and my dentist, no one could figure out what the problem was. I was tested for food allergies, vitamin deficiencies, had head X-rays done, etc... nothing. I tried removing all my usual foods, no more toothpast, or lipsticks, or anything on my face, etc.. etc... nothing really helped. I tried several things, EFAs, flavnoids, antimicrobials, etc... some helped a bit.
Finally, at the suggestion of my family doctor, I tried stopping Leucovorin. He was wondering if this burning mouth syndrome could be a side effect of Leucovorin. I really didn't want to stop it, but after 6 weeks of burning mouth and no solution in sight, I was left no choice.
So what I did is stop Leucovorin (18 mg of folinic Rx), and replace it with 5 mg of L-5-MTHF (Thorne, OTC) and 3.2 mg of folinic acid (Kirkman brand, OTC). The following happened:
1. My burning mouth was much better within 2-3 days.
2. I did not have mood swings, drop in energy, sleep issues, or any stimulation from switching from 18 mg of leucovorin to 5 mg of L-5MTHF + 3.2 mg of folinic.
So now not only I am hopeful I solved my mouth problem, but I am also thinking this new smaller dose and different form of folate will work for me. I had already tried last year to replace 18 mg of leucovorin by 10 mg of L-5MTHF and it had been a disaster. Maybe 10 mg was too much and 5 mg will be the magic number for me. In any case, the lower the dose I can function on, the better, I guess, side-effect-wise.
But we'll see how I do long-term on this. I'll update again in a few weeks.