The structures of heroin and morphine are quite similar, with heroin being formed by acetylation of morphine:
Why is heroin so much more potent than morphine, when their structures are so similar? What biochemical effects lead to heroin's prevalence as a recreational drug, and consequently, the much higher number of fatalities from overdosing on heroin as compared to morphine.
This Source has an attached reference1, which claims the following:
It has been reported that Diamorphine is twice as potent as morphine .
We found no significant differences between the groups over a 24-hour period in the degree of euphoria, nausea and vomiting or sedation, as assessed by subjective visual analogue scores, or in pain relief, nausea and euphoria as assessed by verbal rating. There was, in addition, no significant difference in the requirements for antiemetics between the two groups. Both groups demonstrated relatively low nausea scores. The mean amount of morphine demanded was approximately twice that of diamorphine.
The scientific basis for the alleged superiority of diamorphine over morphine is dubious and since diamorphine is metabolised to monacetyl morphine, and morphine itself, it would be surprising if there were a marked difference. Very few studies authenticate this claim of superiority and the present study is no exception.
This does not explain the prevalence of heroin compared to morphine. Over 15,000 people died in the US from heroin overdose2, whereas the number for morphine is quite less. Are the reasons behind this purely sociological (easier access to heroin compared to morphine), or is there some chemistry that I am missing out on here?