I am 70 yers old and have Parkinsons Disease. Until recently my wife and are have been sexually active. When I began to have erectile problems, initially I used a vacuum pump, but I found these unreliable, Eventually I persuaded my doctor to prescribe Viagra, Which he reluctantly agreed to , giving me 25 mg tablets. These were totally ineffective. It took a great amount of persuasion by my wife and I for him to give me reluctantly, 50 mg tablets. I have found that even with wonderful stimulation by my wife, I was able only to raise a semi stiff erection, which did not last. My question is, would it cause any problems if I took 75mg or even 100 mg Viagra. My health is otherwise very good , my blood pressure is 120/80. Also my penis seems to have shrunk whilst in its flaccid state. Please help as we are unable to discuss this with my doctor, for a variety of reasons.