I've noticed my penis shrinks (when it's flaccid) when I'm on Vyvanse but it hasn't changed the size when it's hard, in fact, I've noticed that I am a lot hornier, I am already a pretty turned on person but when I am on my meds the desire to jerk off becomes more intense. I take around 50-60mg a day (I've been taking Vyvanse for over 3 years now) and I want to start lowering the dosage and I will see if that can help.