L-Theanine

Won't meaningfully reduce stress hormones on its own — one RCT found no impact on salivary stress markers during a high-pressure scenario. Not a proven standalone anxiety treatment; it appears in emerging treatment reviews but lacks large clinical trials for anxiety disorders. No solid human evidence it burns fat, protects your heart, or fixes your gut — those findings come from animal or cell studies only. Don't expect it to replace sleep or act as a stimulant by itself.

• Most cognitive benefits in provided studies come from the caffeine + L-theanine combo, not L-theanine alone — solo effects are modest
• Cardiovascular and metabolic benefits are based almost entirely on animal (mouse/rat) studies — no large human RCTs confirm these effects
• Athlete studies used very small sample sizes (12-37 participants), limiting how broadly results apply
• Products marketed for anxiety, weight loss, or heart health are making claims well beyond what current human evidence supports
• No established long-term safety data from the provided studies — most trials are acute (single-dose) designs