With all the hormones and whatnot inside. Dopamine, adrenaline, melatonin, whatever. Also, there’s this Hunter S. Thompson bit on the… pineal gland?
If it had an effect on you, wouldn’t it be a really messed up high, all over the place? With uppers, downers etc mixed? (Not including the emotional implications of eating raw human brains.)
We don’t actually promote higher levels of dopamine as far as I know. Dopamine agonists work by mimicing what dopamine does to your nervous system. It doesn’t actually produce any more. Also you can be given dopamine intravenously. It is mostly used to raise blood pressure in newborns. But you are right. For other uses, its smarter to mimic it, because of how short it lasts.
We do, however, promote a higher concentration of serotonin with SSRIs. We do that by blocking natural inhibitors that destroy serotonin after being used. This way we can use them more before they die off.