Doxylamine succinate is a non persciption and is used for many reasons, doxylamine has been shown to double the effects of painkillers and such, i would talk to my doc before doing this though, also hydrocodone and codeine are two different compounds.

The reason you are not feeling the effect has nothing to do with the method the drug is being induced by. If you were to crush and snort them it still wouldnt make much difference. My suggestion would be that you talk to your Dr about an alternative and maybe even a switching dose patern which would be like taking one drug for a month then annother for 2 weeks then back to original for another month. Bottom line is narcotics are very easy to build a tolerence to and if you dont give your body time to "forget" the drug it will continue to ignore highe and higher amounts.