Would you mind elaborating on what you've used / your experiences? I'm curious (without wanting to encourage further use) how definite it is that they don't make you high as opposed to that you need higher (no pun intended) doses to get high than other people. Are they effective at relieving physical pain for you?

It wouldn't surprise me if either were true - it's definitely the case that different people need different opiate doses to get the same effects (even for their first dose, not considering developed tolerance), I've known people for whom OTC (over the counter, no prescription needed) cocodamol - 8mg codeine + 500mg paracetamol, x1-2 per dose - contained enough codeine for them to feel a bit high, meanwhile other people like me need prescription strength (30-60mg) codeine to feel any benefits at all, and don't feel remotely high from it.

I also had a friend once who literally couldn't get high from weed, it has no effect on him - at least up to the amount tested, which was him smoking & vaping several grams of a strong strain of cannabis that got the rest of the room extremely high with much less of it. He tried on various other occasions, included edibles from a coffeeshop in Amsterdam, never any effects.