Mucinex DM made my DS(25 at the time) nuts. It's the DM that causes the problem. It was very scary when it was happening. No dextromethorphan for him in any form.
Frankly I don't get any kind of high. Most people need a lot of it to get any kind of effect. However, while it does help with my cough symptoms, I generally feel like someone just jammed something in my throat after taking it.
Mucinex makes me a little jittery and gives me almost a low blood pressure feeling if I don't stay hydrated enough while I'm on it. You really have to keep up on the fluids on that one.
I like Alka Seltzer cold meds, but it has to be the fizzing ones, not the gelcaps.