AddictionBlog has an amazing article by a doctor and recovering morphine addict that describes the experience of injection, rush and withdrawal.
It’s wonderfully written to the point of being painful and if you’re not good with needles, you’ll probably feel a bit queasy when reading it.
Heroin, by the way, is just the prodrug of morphine. In other words, the heroin molecule just gets broken down into morphine in the body and this is the form in which it arrives in the brain.
But because each heroin molecule gets transformed into two morphine molecules (hence the medical name for heroin – diamorphine) the feeling can be a little different because the increased concentration can apparently make the high more intense.
Neurochemically, however, the action in each opioid receptor is the same.
As morphine is used more widely in medicine than diamorphine, it is more likely to be abused by doctors and turn up in cases of addiction.
As we’ve discussed previously, addiction and abuse of medical drugs by doctors is linked to clinical speciality – likely due to both knowledge of and access to particular compounds.
The AddictionBlog article is a strikingly written, honest, detailed and psychologically insightful piece if you want a look into this curious corner of medical drug abuse.
Link to ‘What it’s like to take and withdraw from morphine’
Mind Hacks 
Diamorphine does not become transformed into two molecules of morphine.
Diamorphine is short for diacetylmorphine, as it is morphine with two acetyl, or ethanoyl, groups bound to its ring.
Diamorphine is activated by the body’s metabolism removing these added groups. Diamorphine is a prodrug of morphine, but only one molecule of morphine is formed from each molecule of diamorphine.
I’ve known addicts who get all fetishistic over their paraphernalia, but this guy does it with a special eloquence.
I agree with Dom. You only get one molecule of morphine per molecule of diamorphine.
I’m the unfortunate author, never realised I was being fetishistic; more a type of Pavlovian classical conditioning.
I’ve been clean now ~ 7 yrs, feeling good, tho I had to retire from practice, and miss my patients++, whose support was both wonderful and humbling.
The prognosis for medical addicts is quite good, but I was also lucky to have good people around me.
I’m clean ~ 6 yrs now
http://www.imt.ie/features-opinion/2013/07/the-professional-path-to-recovery.html