I noticed a huge difference on 20 mg. But then I started a couple other medications and I don’t know if that was the cause or not, but the viibryd stopped working. My doctor increased it to 40 mg and I just felt too tired to do anything. My husband is on 40 mg and it continues to work great for him. I had noticed it helped a lot with both anxiety and depression, and at first I thought it was the best medication I’d ever been on.