^^Buddy I know where your coming from, I too am & have been looking for the next Doriden alternative, which I found about too late having started my opioid carreer in 03' by the time it was last available in 2004 it was much too late and I kick myself all the time for it b/c I can't find an alternative since not enough people were dedicated to it as with Qualudes or Placidyl for example but there in case your not familiar simple break down for you, and others too ofcourse. Doriden is a sedative which by itself is said to be quite eazy on the body and not much stronger than Soma or Temazepam, while codeine by itself is a weak to moderate opiate, a pro-drug of morphine which is only a partial agonist. These two relatively weak drugs, Doriden & Tylenol 4 when taken concurrently (at the same time) that is codeine containing pills, traditional combo being called 'Doors & Fours' reffering to the practice of ingesting (orally) 1 or 2 Doriden tablets along with no more than 2 Tylenol 4s or an eqivalent of 120mg codeine (4 T3s lets say) would result not only in a sedating effect like one would get by ingesting a benzo along with their opiate dose but instead of the usual 8%-15% codeine to morphine conversion rate that usually takes place, the Doriden would metabolise the codeine such that the conversion rate of codeine to morphine would increase anywhere between 100%-120% (reason 120% is due to the sedative effect of Doriden itself). This means that 120mg codeine oral with Doriden = 120mg morphine (which is 30% bioavailable orally so it would be like taking 370mg approximatley morphine orally, but in half hour as codeine is faster acting).
I've tried codeine with anyting and everything you can name esp. b/c I suffer from a bad cough I always had some codeine (T3's or T4's) by my side usually taking it semi daily for years while I used various different drugs, always trying to potentiate my codeine. Simple answer, nothing has worked.....except Soma and that only works to a degree but with the codones, oxycodone + soma, codeine + soma are *beautiful* while methadone + soma not so much but still great

just saying the codones work best with Soma.
I've had phenobarbital as well as amobarbital to potentiate it like it should in theory and it didn't at all, rather produced the uwanted effects that I would get from codeine, very little opiate euphoria. Benadryl, Benzodiazepines of every type don't work either except to potentiate the nod or the sedating effects, however Soma is the closest I've come to in my years of research and I've tried tons of bullshit like methacarbamol (Robaxin), Baclofen (worst ever followed by the disgusting after-taste & shit high Imovane/zopiclone) though involving puking with everyone I know.
Haven't tried promethazine but plan to though I can't I'm on MMT and that potentiates codeine strictly, if at all....I have a strong suspicion its just a very sedating, less anti chlornigernic (hallucinogenic) anti histamine similar to Benadryl, but cannot say.
Let me know if u find something!
Good luck!