The best replacement for opium is morphine.

The best alternatives to opium are rated as following:
★★★★★  morphine
★★★★  opiate
★★★  hash
★★  heroin
★  cannabis
★  kratom
★  hashish
  opiates
  opioid
  black tar

Your alternative for opium is not listed? Suggest!
Speaking about opium, one probably shouldn't forget about belladonna.

Other search terms related to opium and their ratings are:
★★★★★ belladonna
★★ hash
★ absinthe
★ poppy seeds
You have in mind a companion for opium and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of opium in all years. Click on graph for more.
opium
morphine
opiate