I've been taking Viibryd for about 4 months and went through the typical dose increase from 10mg, to 20 mg to the typical does of 40 mg. It seemed to be helping really well for awhile. However, now I feel it may be losing its effectiveness. I'm feeling the brain fog and fatigue that it had helped originally. I feel irritable frequently. I missed one dose one day and by 4PM was total irritable and once I figured out that I didn't take that dose and took it, I felt calm again. Has anyone experienced this? So, it seems I'm better on it, but can you develop the need for dosage increase over time? It was hard to find an antidepressant that didn't cause so many annoying side effects. I had minimal side effects with Viibryd and really found it helpful up until about a week or so ago.