I noticed it has a stimulating effect, so just as with the B vitamins, it is probably not a good idea to take it late at night. As I said, I have been using just 10 mg a day, however I think I may switch to 10 mg twice a day. The 10 mg capsules and tablets are almost the same price each as the 25 mg ones, so it would be much more economical to take one 25 mg a day rather than a 10 mg one twice a day. I might switch to 10 mg twice a day first, then when I finished the the 10 mg tablets, switch to 25 mg once a day.