Depends what you mean by hallucinogen. Most psychedelic drugs are prescribed, if I remember right. However, Dextromethorphan (the DM in Robitussin DM) and Diphenhydramine (Benadryl) are both hallucinogenic is high enough doses. DM is a dissociative drug, and Benadryl is a deliriant.
So yes, drink enough cold medicine and you'll get drunk and go on a trip.
I had associates in college who would drink all day, start to de-buzz and run out of beer, then walk to the local Cub Foods and drink a bottle of Robitussin each there in the aisle before walking out with a bag of chips.
Amazing people this stupid could afford to stay in school.