I don't have ED and understand that's it's hence not advisable to take any viagra. But if I take one pill of penegra 25mg or maybe half of it and just once for an experience, will it still cause side effects or will it create any tolerance for erection from tomorrow for using it even just for once ? I want to take it for once only as erection is not as hard as it used to be a year back. And after the influence of drug is gone , will I be able to get normal erection or will it create a tolerance for using it for even one time. Please clear these doubts.