I don't know what effect neurotransmitter precursors have on endogenous production, which is why that information would be useful so we can better judge their safety. The steroid example was to point out that there could be substantial repercussions from taking a substance which you produce naturally. You don't even have to take excessive doses -- take in only as much as you would normally make and your body's production may drop to zero, since it's now being completely replaced. Steroids must be cycled down gradually, because going off cold turkey just leaves you with a crashed endocrine system. If neurotransmitter replacement works similarly, one can imagine a few problems that might crop up with a crashed brain.

> Choline precursors don't seem to have these same "down-regulation" harmful side effects when taken in moderation to bring brain acetylcholine levels back into "normal range."

"Don't seem"? Human studies needed. Maybe these already exist -- that would be handy. I'm not familiar with neurotransmitter supplementation.

Taking something because you have a deficit is indeed different from trying to massively exceed your nominal levels.

In the context of performance-enhancing mental drugs, exceeding your typical levels is of course the point of the exercise.

> "programmer burnout" which likely involved depleted acetylcholine levels in the brain

Possibly, but that assumption seems like it could be quite a leap.

Kind of like saying coffee works because of depleted caffeine levels in the brain. In fact, we have no data on what caused his particular case of "burnout". We can well imagine that an adrenaline shot, cocaine, ephedrine, and many other drugs could well "restore performance", but that doesn't indicate there was a deficit of those particular substances.

Provigil and Ritalin may also help but that doesn't mean there was a deficit of those, either.

An ACh deficit is only one of a bazillion possible reasons for "burnout".