also found this excerpt from wikipedia:

Vinpocetine is also a phosphodiesterase (PDE) type-1 inhibitor,[9] (with an IC50 of approximately 10-5 M.) leading to increases in intracellular levels of cyclic guanosine 3'5'-monophosphate (cGMP), an action that has been attributed to the vasorelaxant effects of vinpocetine on cerebral smooth muscle tissue.[10][11]

Increases in neuronal levels of DOPAC, a metabolic breakdown product of dopamine, have been shown to occur in striatal isolated nerve endings as a result of exposure to vinpocetine.[12] Such an effect is consistent with the biogenic pharmacology of reserpine, a structural relative of vinpocetine, which depletes catecholamine levels and may cause depression as a side-effect of the cardiovascular and anti-psychotic effects.[13]

Side-effects

Vinpocetine has been implicated in one case to induce agranulocytosis,[14] a condition in which granulocytyes - an important type of white blood cell, are markedly decreased. Some people have anecdotally noted that their continued use of vinpocetine reduces immune function. Commission E warned that vinpocetine reduced immune function and could cause apoptosis in the long term. [15]

Dosage

It is recommended that first-time users ingest only 2-5 mg of vinpocetine with meals to make sure they are not hypersensitive to it. Users may then increase the dosage to 10-40 mg a day (which may, although very rarely, cause some light side-effects).