In ADHD, PTSD, seizures, etc. it's not a matter of flow being blocked per se but rather an imbalance in the production of neurotransmitters.

CBD actually reduces dopamine effects.

PPID isn't a problem with too much dopamine. It's too little. There's no evidence that CBD could actually cause this in a normal individual but it might have a significant effect in one that is already abnormal.  CBD does bind to dopamine receptors, just like pergolide, but it blocks the effects of dopamine. I wouldn't give it to a PPID horse.
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Eleanor in PA

www.drkellon.com 
EC Owner 2001