Creatine is converted to phosphocreatine in cells and functions as a fast charger for ATP — the molecule that drives all energy-demanding activity in the body. The brain accounts for about 20% of the body's total energy consumption, and is therefore dependent on a stable supply of phosphocreatine. One study showed that 7 days of supplementation increased brain creatine levels by an average of 9.2%.4

In a double-blind crossover study, 15 participants were kept awake for 21 hours. Those who received a single dose of creatine showed improved short-term memory, faster processing speed, and better logical ability compared to placebo. The effect was visible after 3 hours, peaked at 4 hours, and lasted up to 9 hours. The creatine stabilized the brain's phosphocreatine levels and counteracted the cellular acidification that sleep deprivation normally causes.3

Creatine improved memory compared to placebo, but the effect varied greatly with age. In adults aged 66–76 years, the improvement was large and significant. In young healthy adults, the effect was close to zero.5 This is likely because older adults have lower baseline creatine levels in the brain — and thus more to gain from supplementation. Only about 5% of creatine reaches the brain via the blood-brain barrier, but with regular intake it accumulates sufficiently for measurable effect.2