Save the promethazine for after its fully kicked in, its a CYP-p450-2D6 substrate and will lessen conversion of codeine to its active metabolites if one does it before the codeine bit of the gee's is fully metabolised.
Bear in mind also that it does contain a small amount of squill tincture (Scilla spp. members of the Lilliacea, related to the hyascinths, and bluebells), which contains some cardiac glycosides, its definately fine in that respect at 2 bottles, but if you are on digitalis, or have heart issues it would be wise not to consume it, or limit the dose to at most a bottle, although I never consciously noticed any marked depression of heart rate at 2 bottles of the stuff.