I have a friend who said he was smoking SR-17018 off foil for months and his respiratory system had suffered a lot of damage which in turn directly affected his ability to breathe properly smfh…
Obviously we have almost zero information in parethenral administration in man. I cannot recall if the primate study used parentheral administration but that's the closest we have to a human trial.
I just noted that the pKa of morphine is 7.8-8 so about 76% of it is ionized (i.e. cannot cross the BBB) at physiological pH.
I also checked and the pKa of SR17018 is 9.95-10.15 so only about 99.77% is ionized (i.e. cannot cross the BBB) at physiological pH.
Now as I understand it, if a drug in it's addition-salt form is vapourized, the addition salt is cleaved so your friend was breathing in hydrogen chloride. Decomposition can also take place but whatever the detail, it does rather suggest vaping is a TERRIBLE idea.
But was he at least spared any physical withdrawal symptoms? I suspect not but how severe I could not guess since I have no idea of the quantities and dose intervals. After all, while tolerance developed much slower in the primate model, it still occured.
That is the paradox of weak opioids. Clinicians focus so much on the risk of physical dependence and even addiction, they totally lose sight of the other toxic modes.
But to be clear, this is just a single unstructured case-study. The pKa values are solid as is the fact that vaping essentially 'freebases' the compound but is hazardous. Eveything beyond that is strictly a single example. I don't think there is a study in which the vapour was inhaled so cannot say if this is usual or unusual.
I'm a stickler for stating the limits of knowledge.
But if someone's basic argument is 'it did X and it worked for me', do consider that if the same drug killed others, the unucky one'd don't get to write responses syting 'I did X and it killed me' - this is called survivorship bias. Even in dilute forms, people will tend to overstate benefits if something works for them far more often than a person even stating it didn't work for them - especially when addiction is at play. Some people are just wired so addiction is more likely - it's not a character flaw, it's genetics and childhood experiences.