I took it for almost three years. It was part of a herbal mix given to me by a well-known medical herbalist. The three herbs were targetted at adrenal fatigue. The other two were ashwaghanda and shatavari. Gotu kola is one of the highest herbs in levels of vitamin B.
However, it's important not to take it for too long (as I did): it can affect the liver after a while.