A lot of this depends on locale -- firstly, presumably the poison in the fixed-combination products is paracetamol, but it is added to them combos not because of anything nefarious like the US law of 1943 that mandated adding those things to hydrocodone, but because people who have colds, flu, &c (and need codeine, DHC potentiation) benefit from it and/or aspirin,. In the US and Canada, there are NyQuil and Alka-Seltzer Cold Medicine which come in different formulae and have lot of local and generic equivalents . . . but DXM is also available by itself in syrups and gel gaps and tablets too,, and with and without the paracetamol, antihistamines, and the decongestants, which tend to be phenylephrine, ephedrine, and pseudoephedrine . . .
For those who get nauseated by codeine or other narcotics, try mixing doxylamine with niacin and dicycloverine (Bentyl) and perhaps a small dose of paracetamol if you want it to help you get to sleep too. Washing it down with Coca-Cola, Pepsi, RC, Sprite, 7up, Slice or whatever really helps too -- especially Cherry Coke.
It may be best to get the pure ingredients and mix and match:
Doxylamine Succinate -- Some local sleeping aids
Diphenhydramine -- Benadryl inter alia
Phenyltoloxamine -- Reportedly some local brands
Orphenadrine -- Norflex
Orphenadrine + Aspirin -- Norgesic
Dimenhydrinate -- Dramamine
Meclozine -- Dramamine II
Pyrilamine + Paracetamol -- Midol
Dextromethorphan -- Robitussin plain, plain gel caps, generic DXM
Chlorphenamine -- Chlor-Trimeton
Dexchlorphenamine -- Polaramine
Bromphenamine -- Dimetapp
Dexbromphenamine -- Drixoral
Desoxyphenamine -- Actifed
DXM + Chlorphenamine (30mg/4mg) -- Coricidin for High Blood Pressure -- a round biconvex filmtab. The oblong Coricidins may have paracetamol