The study adds more evidence that "human beings simply aren't built to handle feeling that good," Fleming said. By hyperstimulating the pleasure center, "a new huge craving is induced that people who have never tried it can't understand and those who have — even those who are clean — never really forget,"

Vargas-Perez said it's no wonder that drug users who hyperactivate the pleasure center almost immediately feel the urge to do so again. The research provides clinical evidence of why it takes higher and higher doses of a drug to induce euphoria, and why euphoria quickly turns into a dependence that becomes an extreme feeling in users that they are incapable of feeling normal without the drug, he said.

As the study puts it, chronic drug users, as noted by previous research, can experience an increase of a naturally occurring brain-derived neurotrophic factor or BDNF in the ventral tegmental area. A single injection of BDNF made rats behave as though they were dependent on opiates they had never been given. Although rats instinctively prefer certain smells, lighting and texture, these rats left their comfort zone in search of a fix.

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