Depends on drinking. How much of what, and what otc drugs you are talking about. Anything that is potentially sedating, like antihistamines that are in cold/allergy medications or otc sleeping aids, can cause major problems when taken with excessive amounts of alcohol. If we are talking 1 or 2 standard drinks, probably few if any problems, but higher doses of alcohol can cause harm.
It depends on the me. If a person is drinking alcohol and is taking prescription medication or even over the counter medicine at the same time, it can sometimes make a person get very sick with nausea and vomiting. Other side effects may be to cause central nervous system depression-your mind gets sleepy and you don't think as clearly as without the medicine. Your reaction time may also be impaired/slower.