Diacetylmorphine is purported to produce more euphoria than other opioids upon injection. One possible explanation is the presence of 6-monoacetylmorphine, a metabolite unique to diacetylmorphine. While other opioids of recreational use, such as codeine, produce only morphine, diacetylmorphine also leaves 6-MAM, also a psycho-active metabolite. However, this perception is not supported by the results of clinical studies comparing the physiological and subjective effects of injected diacetylmorphine and morphine in individuals formerly addicted to opioids; these subjects showed no preference for one drug over the other. Equipotent injected doses had comparable action courses, with no difference in subjects' self-rated feelings of euphoria, ambition, nervousness, relaxation, drowsiness, or sleepiness.
Short-term addiction studies by the same researchers demonstrated that tolerance developed at a similar rate to both diacetylmorphine and morphine. When compared to the opioids hydromorphone, fentanyl, oxycodone, and pethidine/meperidine, former addicts showed a strong preference for diacetylmorphine and morphine, suggesting that diacetylmorphine and morphine are particularly susceptible to abuse and addiction. Morphine and diacetylmorphine were also much more likely to produce euphoria and other positive subjective effects when compared to these other opioids.