You are right to be concerned about this situation; it is very serious. While these issues need to be dealt with with great sensitivity and care, such issues also warrant an intervention.  Not only can alcohol interfere with his medications, but the effects of the alcohol can aggravate symptoms, such as confusion or drowsiness.  Additionally, driving while under the influence is illegal and this behavior is risky on many levels.  You may wish to involve your husband's physician in this matter, perhaps enlisting his help in not only getting your husband to cut down on his drinking, but to cut down on the driving as well.  Depending upon the level of his cognitive impairment, it is possible that your husband should not be driving at all anymore.  As your husband may not want to hear these things from you directly, enlisting the assistance from a neutral third party, such as his physican or a trusted neighbor or friend, may be an option you wish to explore.