Why does topamax (topiramate) cause memory problems& fatiguing is my dose high 25mg 2x a day? Can it cause permanent problems? Is it safe?

Yes it is safe. Topamax (topiramate) can cause fatigue early stage of taking it and may go away after few days, same goes for memory problems.If the side effects persist, you should discuss with your doctor and he/she may change your med or reduce the dose.It does not cause permanent problems with long term use.
Due to actions. Topamax (topiramate) blocks a glutamate pathway in the temporal lobe important for short term memory, and in fact, is dosage dependent, and if you are experiencing side effects at such a low dose, unlikely that you will do well if dose pushed into therapy range. Talk to your doctor. Yes, indeed reversible and safe, but may not be best drug for you!