ADD here, sans hyperactivity, 27 years old. I haven't tried meds in about ten years but recently decided to give it another shot.
I first tried Adderall - 10mg morning, 10mg after lunch, for about six weeks. I noticed a slight increase in horniness but its kinda hard to tell because I've always had a high sex drive and frequently masturbated (thanks, low dopamine levels!). Immediately after starting the drug I found it somewhat hard to get and maintain an erection. My GF and I have only hooked up a few times in the last few weeks for unrelated reasons, but I was just barely able to keep it hard whilst performing less-than-my-favorite positions, something I have never experienced and certainly should NOT happen when I'm really excited to get laid. It also seemed like I came less both in volume and intensity of contractions. It sucks as a catch-22 because for most of the day I feel like I really need to spank it, but can't get it up well and don't have a solid mind-clearing orgasm, so there's very little relief and the cycle continues.
I switched to Vyvanse a week and a half ago because the Adderall was starting to make me a little aggro. I would say Adderall made me feel slightly irritable like when you're coming down from a coke high, and I had to keep that in mind and catch myself before I would say something mean for no good reason. I didn't notice it as a major problem, but after my GF told me it was actually really noticeable and starting to scare her, I knew I couldn't continue. Since switching to Vyvanse, I'm seeing the same issues with sex drive and getting an erection, but the behavioral problems are gone, which is good.
Vyvanse is time release and I feel the "high" for a solid 10 hours or so, and the sex drive/erectile problems seem directly proportional to how much I am feeling the meds. I also didn't have any problems for the 8 days I was clean between switching meds. So it seems to be an immediate problem that only occurs when the drug is in your system and immediately goes away afterwards.
Hope this helps, I'll keep an eye on this if you have any questions on my experiences.