I've not been on viagra - I went straight to Cialis, but I know there are other people on here who have happily interchanged them. I think, given how much longer it lasts than Viagra, I think you'll be pleased with the results. It was a massive relief for me, let me tell you. Not having to think about my 'issue' all weekend!
Apparently Cialis has less side effects, but both of them do share the potential side effects of back pain and muscle aches. Both Cialis and Viagra have the same active ingredients, so if you're approved for one you should be approved for the other, so its no big deal to switch between them. It's common to go for viagra during the week and cialis on the weekend