Glutamatergic

L-theanine is an amino acid found almost only in tea. Taken at 200 to 400 mg a day, it may reduce stress and anxiety in people under stressful conditions. Its best-known use is alongside caffeine, where the pair improves attention switching more than either alone. A 2025 meta-analysis found small improvements in subjective sleep.

Piracetam is the original "nootropic". C. Giurgea developed it in the late 1960s and coined the word to describe it. It is licensed in several countries for cognitive disorders, vertigo and cortical myoclonus. The evidence is mixed. An older meta-analysis found a global benefit in older adults with cognitive impairment, but a 2024 meta-analysis could not confirm an effect on memory.