L-THEANINE
An amino acid found in green tea that promotes relaxation without drowsiness and may enhance focus, especially when combined with caffeine.
Multiple randomized controlled trials demonstrate that L-theanine at 200-400 mg/day reduces subjective stress, anxiety, and sleep latency while improving sleep quality in healthy adults. EEG studies confirm increased alpha-wave activity within 45-60 minutes of ingestion, indicating relaxation without sedation. Combined with caffeine, L-theanine improves attention-switching speed and accuracy more than caffeine alone, suggesting synergistic cognitive enhancement. Evidence for standalone cognitive enhancement is weaker, with benefits most apparent in individuals with baseline cognitive impairments or elevated stress. Long-term safety data remain limited, though no serious adverse events have been reported in clinical trials lasting up to four weeks.