I took my prescribed 30mg of vyvanse (lisdexamfetamine) approximately 7.5 hours ago, is it safe to take a mucus relief dm (dextrometorphan hbr 20 mg, guaifenesin 400mg/ expectorant) right now?

Yes: Assuming you take no other meds, combining Vyvanse (lisdexamfetamine) with Mucus Relief DM shows no significant drug interactions. Hope you feel better.

I would think so: Derek, I do not believe that you should have any trouble. The two should not interact with each other and I am not aware of any concerns. I am glad that you are cautious with possible interactions. Wishing you the best.