erectile dysfunction

dear dr

I met my partner just after he had donated a kidney to his son. We have a non-exististant penatatrive sex life. He says he cannot sustain an erection because of lack of feeling in his nether regions. My question to you is twofold:
1. if his erectile dysfuntion is physical rather than psychological, do you think Viagra would help?
2. If he has had a kidney transplant and is overweight, would it be unrealistic for him to take viagra on a long-term basis? Your advice would be greatly appreciated. Kind regards Janet