I'm submitting an answer to add some more body to the statement that Gabapentin causes erectile problems.
I've been taking 2400mg of Gabapentin daily for 2 years and will probably continue to do so for the rest of my life. I take it to reduce the effects of Nystagmus (google if you're curious!). It works wonderfully and has changed my life for the better.... mostly.
I am able to hold an erection but it can be difficult and never very hard. Certainly hard enough for good sex but not as hard as I'd like. Generally it takes a lot of effort to climax and can get a bit, errrmm, rough? . I dunno, but it's can be very frustrating for me. Gladly it doesn't worry my wife.
Sensation is greatly reduced by the medication which is why it's tough to climax. In my experience the side effects only last as long as the benefit of the meds. I take it 3 times daily and it works for about 5hrs. I definitely get more enjoyment from sex first thing in the morning as it's 10hrs since my last dose. If I want better sex I miss a dose then take it after - which is easier with my condition than it would be for others - however, trying to predict when my wife will be up for it is probably the biggest issue lol.
Unfortunately there is no alternative medication for my condition, in fact this isn't even signed off as an official treatment as it's still under long term trials.
I'm gonna speak to my GP about trying viagra (pretty embarrassing for a 32yr old) but having read a comment above I'm not confident that it's gonna help.
Anyway, keep at it guys. Get heavy handed if you have too, or if you can delay a dose that might help. I find that thinking and worrying about it makes things worse, so try to clear your minds and go with the flow <!--[endif]-->