Butterbur for Migraines

Andreas,
Do you know anything about Butterbur for Migraines. I have Migraine Associated Vertigo and my head feels full, swollen and inflammed constantly as well as a constant feeling of off-balance or rocking on a boat. I have got to have some help for this. The Neurologist has tried many migraine preventatives but I just don't tolerate meds or herbs or vitamins very well. I was thinking of trying Butterbur but I read on Dr. Andrew Weil's site that there is an ingredient in Butterbur (Pyrrolizidine Alkaloids - PAs) that is very toxic to the liver. How would I go about finding a safe brand?
I am doing liver flushes and colonics and eating gluten free but don't seem to be improving.
I have read your book "The Amazing Liver Cleanse". Tweet