It is true that the conventional wisdom is that dopamine itself has no therapeutic benefit for PwP because, as others have said, it cannot cross the BBB.

You can leave it there or you can see for yourself.

I have tried to measure the impact of dopamine on a PwP (me), see the thread from three years ago, "Fermented Banana": http://neurotalk.psychcentral.com/thread164365.html

I don't have a source of pure dopamine, so I used banana because its skin contains high levels of dopamine. I used fermentation because Aunt Bean had reported good results with fermentation.

My conclusion was:

"On the basis of limited data (3 tests of the fermented mix, plus control tests), a large helping, made from 500 ml yogurt and two medium bananas, has for me a symptomatic effect similar to that given by approximately 25 mg levodopa."

So, it wasn't a practical therapy for me. But, my results do not close down the possibility that dopamine does have an effect. Perhaps, as others have suggested, the BBB in PwP is compromised; perhaps dopamine can work via the ENS. Alternatively, perhaps my measurements were incorrect (they were based on the side to side tap test) or subject to a placebo effect or, perhaps, the effect was real but caused by something else in the banana skin.

John