Codeine is metabolized to morphine, so it's not really 'in-between'. Plus it's a bad painkiller due to variability in pharmacokinetics. Good practice would be to not use it anymore.
Now, there also is stuff such as tramadol (WHO ladder step 2). But it also can be abused, and is indeed sold on the streets.
"Codeine is metabolized to morphine, so it's not really 'in-between'. Plus it's a bad painkiller due to variability in pharmacokinetics."
Right, and as you say it'd be a good practice to stop using it, especially if it's OTC, which, as mentioned above, it still is in some countries.
It used to be OTC where I am but it's now only available by script. I recall decades ago taking combination codeine/paracetamol (aka acetaminophen) for headaches and the codeine definitely exacerbated them, moreover it was not very effective as a painkiller.
It turned out that whilst paracetamol wasn't very effective by itself the headaches didn't rebound as they did with the codeine mixture. All up, NSAIDs—aspirin, ibuprofen—were better even though they caused minor stomach upset.
Opiods are available at many different magnitudes of strength.
For instance, on a per milligram basis, Oxycodone is about 1.5 times stronger than morphine.
Codeine, which is actually available OTC in some countries (Including Canada, but NOT the US), is about 1/20th as strong.