As has been said, it's almost a guarantee for blackouts. At some point one either forgets how much one had taken or overestimates the amount of control, thinks not to be high enough and decides to take a few more. Then with some bad luck you decide to go for a ride and wake up in an arrest cell or padded room.
In other times I loved to combine alc + lorazepam (just 1mg) and took DXM almost daily. Got the scenario above, I miss complete 10 days and my car including license was gone. Don't do it.