How long before the side effects start to decrease? I'm taking an antidepressant.

It is possible that if you switch back to Viibryd, you may experience some initial side effects again. However, they may not be as intense or last as long as when you first started taking the medication. Nausea can persist for up to 14 days, but typically side effects are more pronounced in the first two weeks and then start to diminish. If you are having a difficult time tolerating Trintellix and experience negative effects with Viibryd as well, it may be best to consider trying a different medication altogether for optimal treatment. It would be a good idea to discuss this with your doctor before making any changes.