Creatine's slow uptake into neural tissue
The brain uses the creatine and phosphocreatine system to buffer ATP much as muscle does, helping maintain energy supply when demand spikes. Brain creatine, however, is partly produced locally and crosses the blood-brain barrier slowly, so raising brain creatine with supplements is more gradual and less complete than raising muscle creatine. This kinetic difference is one reason cognitive effects, if present, take longer to appear than muscular ones.
Supporting neuronal ATP availability under load is the proposed mechanism for any cognitive benefit, rather than a direct stimulant or neurotransmitter action.
What the cognitive evidence currently suggests
Studies most consistently suggest benefit under conditions of energetic stress, such as sleep deprivation or demanding mental tasks, and in people with lower baseline creatine, for example some vegetarians. Effects in well-rested, omnivorous adults are smaller and less certain, so this is an area of active but unsettled research.
This is general educational information, not medical advice. Consult a qualified professional before using creatine for cognitive purposes.