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.)
I think melatonin is more the exception than the rule.
Testosterone needs to be injected and has a very short half life.
A quick Google shows Dopamine also needs to be injected and has a half life of one minute, so is only used as an IV drip.