L-theanine is an amino acid found primarily in green tea, and there is growing scientific interest in its potential to alleviate symptoms of anxiety disorders. The evidence supporting its use comes from both preclinical and clinical studies, though the overall quality and quantity of research remains moderate. L-theanine is thought to modulate neurotransmitters in the brain, including increasing GABA, serotonin, and dopamine levels, which may promote relaxation without sedation. It also appears to reduce physiological markers of stress, such as heart rate and cortisol levels.

Several small-scale, double-blind, placebo-controlled trials have demonstrated that L-theanine supplementation can reduce subjective feelings of anxiety and stress in both healthy subjects and those with mild anxiety. For example, a 2019 randomized controlled trial published in "Nutrients" found that 200 mg/day of L-theanine for four weeks significantly reduced anxiety and improved sleep quality in individuals with stress-related symptoms. However, studies specifically targeting diagnosed anxiety disorders are fewer and often limited by small sample sizes and short durations.

Overall, while there is scientific support for L-theanine’s anxiolytic (anxiety-reducing) effects, especially in acute stress situations, more robust research is needed to confirm its efficacy as a treatment for clinical anxiety disorders. It is considered generally safe and well-tolerated, making it a popular adjunct or alternative to conventional treatments, but it should not replace evidence-based therapies for anxiety disorders without medical supervision.