Several sparse studies have been conducted over the years regarding the effects of consuming these substances concurrently, especially studying psychomotor activity, with minor deviations in conclusions drawn.
The first double blind study (Consroe, et al) showed that alcohol and CBD consumption lead to lower levels of blood alcohol content and lower impairment levels of the cognitive and psychomotor systems.
The second study (Belgrave, et al) found there to be minimal differences in taking both substances at the same time, only noting that alcohol was the clear intoxicant and CBD had no discernible effects on the participants mood or abilities when taken alone. However, additional information tells us that because both CBD and THC are liposoluble, they dissolve in alcohol and are absorbed at almost twice the rate into the bloodstream when consumed within several hours of one another or concurrently (Lukas, 2011).
It is always wise not to mix medications and alcohol, but according to the current findings it should not be an additional risk to those taking CBD unless they have underlying medical causes that would make it wiser not to imbibe.