Yeah the active compound in robitussin is actually a powerful hallucinogenic. Some people take large amounts to get high, and it's called robotrippin in slang (no joke). I've heard it may cause brain damage though so I never messed with it.
Yeah. It has dextromethorphan in it. If you take around 2,3 hundred mg's you will trip at somepoint, you start out high and than you trip. Not even that much mg wise will fuck someone up. Not necessarily trip, but you'll get high.