I started taking it for migraines and had the added benefit of being able to go off the other mood stabilizer. It has helped with racing thoughts and stabilized out my rapid cycling. It does help me to sleep at night, will feel groggy then as take it at night, but I wake up refreshed. I am happy with this as I have trouble sleeping most nights otherwise, insomnia is a real problem otherwise. I have not experienced the "fog" everyone is describing but the higher I go, I do have problems with specific word recall. It is not permanent; if you back off the dose, the ability returns.