Opioid and psychostimulant addiction share a common action of causing massive dopamine release in the nucleus accumbens.

“So cocaine and methamphetamine, what the drugs known as psychostimulants, actually bind to a protein in the brain, or a molecule in the brain that is responsible for sucking up. It's a vacuum cleaner sucking up the dopamine after it's been released. And cocaine prevents that dopamine from being vacuumed up. So the cocaine hangs around longer. Meth not only prevents the dopamine from being vacuumed up, it actually causes the reverse. It actually causes the direct release of dopamine from what we call nerve terminals, from the site where dopamine is released.”