“From the brain” is basically like saying from this impenetrable black box.

Medications do not work the same on people with the same conditions. You could have exactly the same depression/anxiety symptoms as another person but have a completely negative reaction to an SSRI that works perfectly for them.

Some people with ADHD can still get high on certain stimulant meds if they take a high dose, but some (like me) don’t get anything but a headache.

For most people, drinking alcohol is a slightly euphoric experience that decreases inhibitions and makes them feel relaxed. For others (like me) it does nothing or it makes me anxious.

Now the physical effects do exist in that latter case; my heartrate and breathing do slow if I drink a lot. But the subjective experience is quite the opposite of what its “supposed” to be.

If you want to feel physically alert, injecting yourself with epinephrine would likely do the trick. But if you want to feel more “manic” as in lacking impulse control, feeling rapid emotional changes, and feeling alert. You likely need a cocktail of drugs specifically tuned for your brain.

There is no single part of the brain controlling anything. I mean literally anything. There are lots of areas that are involved with certain actions like the hippocampus with memory and V1 with visual input but there are basically no processes that are comtrolled solely by a specific part of the brain.

And what makes it even more complex is that every part of the brain is recieving different information from thousands of different neurons scattered across the whole neocortex. Some of these connections seem to follow a general trend, but if you’ve ever seen a rabies tracing experiment you’ll know that basically every part of the brain has at least one or two connections from any other part of the brain regardless of function.

Your brain is a chaotic mess and what little organization exists might not even be necessary. There are mice called Reeler Mice who lack a specific glycoprotein (reelin) which is responsible for organizing the brain into layers. As such, their neurons are scattered all around rather than forming the neat layers and patches that typical mice have. Guess what is wrong with these mice behaviorally? Nothing. apart from the motor issues caused by an undeveloped cerebellum (part of your brain that coordinates muscle movements) they are basically normal mice. (I should note there is some research on reelin levels and relation to psychiatric disorders, but its not well studied and inconclusive)

You could have a completely different brain than any other human on earth and still function like a normal human. There are people without a corpus collosum (the largest white matter tract in the brain, connecting both hemispheres) who are asymptomatic even though most people with the condition get seizures. There are parts of your brain that might not exist in others like the massa intermedia; and there are no signs whatsoever until you do a scan.

It is likely your brain is laid out in a unique way that is unlike any other human. Maybe it can carry out processes and emotions and actions the exact same way someone else’s does, but that does not mean both brains are doing that process in the same way. So it is never guaranteed that a drug or stimulation in a specific area which causes the desired effects on one person will cause the same effect on another.

And the more complex the desired outcome is (e.g. “mania” rather than just “alertness”) the less general your “solution” will be, meaning it will need to be tailored to each subject more specifically.