I've used it frequently, as one of my attendings did some of the original research on it. It either works or it doesn't. Some of my patients have shot up like a cork when nothing else seems to have worked. The results have typically come on pretty quickly, as well. If you have samples of it, it works beautifully. Give them the samples, have them take 15mg daily, and come back to see you in 3-4 weeks. If they aren't feeling better, it's probably not going to work, and you start with something else. If it does, well, you have some answers. I had one patient on Cymbalta 120mg daiy and Abilify who had been on multiple trials of antidepressants with only modest results. I put him on Deplin, and when I had seen him he was feeling great, had stopped his Abilify, and he has been in remission since.
Roughtly 70% of depressed patients have a dysfunction at the MTHFR enzyme. Throwing folic acid supplements into the fix isn't going to help and may worsen symptoms because you're blocking transporters that might actually transport l-methltfolate.
I've actually had some success using Deplin to treat anxiety, as well, on roughly 3-patients. They were having SSRI poop-out syndrome, and I tossed in a bit of Deplin and they got remarkably better.
It's expensive. Studies have typically shown you need 15mg daily to get a sufficient effect, as 7.5mg didn't work. I've had a few patients who got modest to good results at 7.5mg daily and have cut the 15mg tabs in half to save expenses, with it roughly costing them $45 per month at that rate. Otherwise it's $90 per month, as insurance just doesn't often cover it.
Some are willing to pay that amount, as it works and without side-effects from those who it benefits. Others it has not effect on whatsoever (where you'd surmise they don't have a deficiency).
I consider it a third line agent that I start consideing more once you've augmented an SNRI with only partial improvement or in someone who has the "poop out" effect.