Key Takeaway
Systematic review of 9 studies finds L-theanine supplementation (200-900mg/day) improves anxiety, sleep quality, and cognitive function in patients with mental disorders including schizophrenia, GAD, and MDD.
Summary
This 2024 systematic review examined all available clinical evidence on L-theanine supplementation in patients diagnosed with mental disorders. The authors searched PubMed, Scopus, Web of Science, and Cochrane databases, identifying 9 eligible studies (7 RCTs and 2 open-label trials) covering conditions including schizophrenia, schizoaffective disorder, generalized anxiety disorder (GAD), major depressive disorder (MDD), and ADHD.
The review found consistent evidence that L-theanine at doses of 200-900mg per day improved multiple outcome measures across psychiatric conditions. In schizophrenia patients, L-theanine as an adjunct to antipsychotics reduced anxiety and improved sleep quality. In GAD patients, adjunctive L-theanine improved anxiety symptoms and sleep quality. For MDD, L-theanine supplementation alongside antidepressants showed improvements in depressive and anxiety symptoms, sleep quality, and cognitive function.
The authors concluded that L-theanine appears to be a safe and well-tolerated adjunctive treatment for mental health conditions, with benefits spanning anxiety reduction, sleep improvement, and cognitive enhancement. However, they emphasized the need for larger, well-designed RCTs to confirm these findings, as most included studies had relatively small sample sizes.
Methods
Systematic review following PRISMA guidelines. Searched PubMed, Scopus, Web of Science, and Cochrane Library up to August 2024. Included clinical trials (RCTs and open-label) studying L-theanine supplementation in patients with diagnosed mental disorders. Nine studies met inclusion criteria: 7 RCTs and 2 open-label trials. Quality was assessed using Cochrane risk-of-bias tools.
Key Results
- 9 studies included covering schizophrenia, GAD, MDD, and ADHD
- Doses ranged from 200mg to 900mg per day across studies
- Schizophrenia: L-theanine (400mg/day) as adjunct to antipsychotics reduced anxiety and improved sleep quality
- GAD: L-theanine (450-900mg/day) improved anxiety symptoms and sleep quality
- MDD: L-theanine (250mg/day) alongside antidepressants improved depressive symptoms, anxiety, sleep, and cognitive function
- No serious adverse effects reported across any included studies
- L-theanine was well-tolerated in all populations studied
Limitations
- Small sample sizes in most included studies
- Heterogeneity in dosing, duration, and outcome measures prevented meta-analysis
- Only 2 databases yielded most results; limited grey literature search
- Some studies had moderate-to-high risk of bias
- Short intervention durations (most 8-10 weeks)
- Publication bias cannot be ruled out