Those are low doses of each. I wouldn't worry unless u weigh like 75LBS and are allergic to them.... Ive never mixed them but ive done over 100MGs of flexiril and over 1400MGs of DXM.... im still here... i dought youll trip or even feel much from 300MG. id say 600MG starting dose.... how much u weigh / height / etc... depends on how much to go.....