I discovered something by accident that I couldn't find reference to here, so I thought I'd throw it out
I receive markedly fewer (less than half, to a third) dragon bites while smoking opium if I am currently "in the fog" from smoking hemp.
My first "crazy high" on opium gave me over 30 dragon bites - but while "in the fog" I haven't gotten over 12 bites getting crazy high on opium.
(I discovered this when I had a "get high on opium" quest while still in the fog from a previous "get high on hemp" quest)
I've tested this several times while doing credos and it seems to hold (as long as the fog doesn't run out first!)
Maybe you guys already knew this? Anyway, I found it quite helpful. Hemp first, then opium!