i don't see why they wouldn't be safe to use at home... my only concern would be that you would become dependant on them? which really isn't good if your bowels are functioning regularly... you'd want to keep it that way!
i'm really not sure about the metabolism thing, sorry, maybe try searching it? i had no luck though!
i know that like, people do it and stuff to flush out their system... they also do like, colon flushing and stuff to lose weight and all... i'd talk to your doctor about it for the best answers!