If you are talking about toxicity, there are no known drug interactions between THC and Vyvanse. Key words being "none known." I.e that doesn't mean that there aren't, we just don't know of any. That said, given their mechanism of action (Vyvance is a stimulant/dopamine norepinephrine reuptake inhibitor and THC acts on the anandamide receptors), I would not expect them to interact in a way that would result in toxicity/physical harm to you if you did pot while on Vyvanse but the effectiveness of Vyvance may be compromised.