And this was the reason advanced for using Heroin instead of Morphine. For the same amount of pain relief Heroin causes less constipation than Morphine. I personally never heard or read anything about Morphine making you less lucid that Heroin – it was the other side effects that mattered.
I am not a doctor. I do not do palliative care. What I know is far out of date. It might have been just common belief even then. I have not looked this up recently. There are many new opioids. etc