There is an excellent diagram in Nature Neuroscience that shows how the various drugs of abuse share a common pathway, usually starting in the ventral tegmental area and progressing to the dopamine neurons in the nucleus accumbens.
This highly technical article accentuates the point that all substances of abuse increase dopamine, remove pain and promote pleasure. The PURSOR protocol also increases dopamine but rather than increasing it very rapidly, does it relatively slowly, seconds vs. milliseconds. PURSOR relieves the psychic pains of low dopamine but provides no rush of pleasure. It therefore is not addictive.