As I understand it, oral medications (eg Viagra, Cialis) require some nerve function to do their thing. They work on the blood supply aspect of the erection. With no nerves left, those meds don't function, so I've never even tried them.
However if I ever see any evidence of natural erections, and one year out, I don't -- that would indicate some nerve regrowth, so then I would be tempted.
So my opinion -- probably a waste of time (and money!) now, but don't rule them out in a year or two.
Another option that can work well in the non-nerve-spared are penile injections. Scary at first, but I find the results are well worth-while.
Age 63. Other than cancer, in good health; BMI 20
Pre-op: No symptoms; PSA 5.7; Gleason 4+5=9; cancer in 4 of 12 cores
7 March 2008, RRP, non nerve sparing
Two nights in hospital; catheter and staples out after 7 days
Continent, no pads needed from the get-go
Post Op: Stage pT2 M- N-; clear margins and lymph nodes; Gleason 4+4=8; prostate weight: 37gm
6-week and 7-month PSAs: 0
Bimix injections working well