i've done it... twice. both occassions 700mgs DXM in the morning, 1 pill of MDA in the evening (about 6 hours of sober space in between).

if you take the x immideatly after a dxm peak, i can see seratonin syndrome occouring (happened to me with a 5-HTP mix up on a dex comedown)... but nothing observingly bad happened to me when i took the x 6 hours after the dex on both occassions.

but i still wouldn't recommend it for you brain's sake