I think it was originally written take one twice a day and then the dr said I could take all of it at night. I was having a lot of vomiting from lamictal at the time and I think partly the goal was just to keep my lithium in (the vomiting was in the morning) but also it was easier to handle that way. It was harder to get levels drawn at 11 Am than it was when I had 12 hours after a PM dose but otherwise it worked fine. But the formula you're on probably matters whether this is ok and some drs probably have different concerns than mine did. HOwever if you're allowed to take it all at night you miss out on a lot of side effects although you do have to pee at night more frequently. I got to do that in my sleep almost.