I don't remember if it makes me groggy or not; it's been since 2007 or so since I've taken it. I credit the humidifier I run at night in the bedroom if I've got a cold for reducing the length and severity of my coughing with colds: it's probably not a coincidence that I got this way now, when I didn't have one in England and failed to run it after coming back (except for the last two nights, that is!).