Most explanations of brain fog reach for a neurotransmitter. Low dopamine. Rising serotonin. Faltering acetylcholine. Those names show up because they are what we know how to measure, not because they are the cause. Underneath all three is a simpler problem: the cells that do the thinking are running short of fuel.

The fuel is ATP, the small molecule cells use to power almost everything they do. A neuron that cannot make enough ATP cannot fire on time, cannot recover between firings, and cannot maintain the charge differences across its membrane that make signaling possible. The neurotransmitter shifts that everyone talks about are downstream of that.