It seems that the feelings heroin addicts experience when they take the drug is not an unfamiliar sensation at all. In fact, that sensation is similar to the one a person experiences when they orgasm. A recent study published in Journal of Neuroscience stated that the brain activity of a person using heroin and the person experiencing an orgasm appear to be the same.
When heroin is ingested either through inhalation or through IV, it triggers a chain of events that lead to the release of endorphins in the body. Since heroin has a similar chemical structure to opioids, they bind to the opioid receptors in the brain and cause the body to undergo pain relief, improvement of mood or stimulate the feeling of euphoria as levels of dopamine in the brain increases.
This same euphoria is experienced when a man or a woman achieves sexual gratification in the form of an orgasm. During this experience, the brain undergoes various activations and deactivations. The strongest activation is seen in the mesodiencephalic transition zone that includes amongst other features VTA. This VTA contains the dopaminergic group of cells which deal with the release of dopamine and therefore plays a vital role in rewarding behaviors. This VTA activation is also seen in cocaine and heroin users which solidify the correlation between orgasmic pleasure and heroin. It also explains why those who regularly consume heroin have an overall suppressed sexual drive, since they are experiencing the feeling of orgasmic pleasure through heroin.
Another region in the brain, lateral orbitofrontal cortex, has a recorded decreased activity during orgasmic pleasure. This is the center of the brain that deals with reasoning and control of behaviors. Moreover, activity in amygdala which plays vital role in causing vigilance and fear is also decreased, especially in women. These decreased activities therefore result in the person acting rash and unafraid, a deactivation that is also observed in heroin or cocaine users.
While other brain activities may well be involved in the feeling of euphoria experienced during an orgasm, this study helps in improving our understanding of what pleasures the brain provides in such circumstances and also highlights why people continuously seek out drugs such as heroin or cocaine.