Does L-Theanine Help Anxiety and Depression?
For depression, one small trial looked promising when L-theanine was added to an antidepressant. For generalized anxiety, the one trial found no benefit over placebo. A systematic review in BMC Psychiatry gathered 11 randomized controlled trials of L-theanine, an amino acid found in tea leaves. The authors concluded that it reduced symptoms more than control conditions in people with schizophrenia, anxiety disorders, and ADHD. The single trials in depression and obsessive-compulsive disorder (OCD) also looked positive when L-theanine was added to an antidepressant. But the evidence is thin. Most conditions had only one or two small trials, and the one trial in generalized anxiety disorder found no benefit for anxiety over placebo.
The review describes several ways L-theanine may act on the brain. It may raise levels of GABA, a calming brain chemical. It may also affect serotonin and dopamine, and it has been linked to more alpha brain wave activity, which goes with relaxed alertness.
What the data show:
- Depression (one trial): Added to sertraline, L-theanine led to remission in 68% of patients versus 32% on placebo plus sertraline
- OCD (one trial): Added to fluvoxamine, 92% had a complete response versus 36% on placebo plus fluvoxamine
- Schizophrenia (four trials): Added to antipsychotics, it reduced some symptom scores, including anxiety and general psychopathology
- Generalized anxiety disorder (one trial): No extra benefit for anxiety over placebo, though sleep satisfaction improved
- Doses: Most trials used 200 to 450 mg a day
- Safety: Generally well tolerated, with no serious side effects reported
The review searched six databases through June 2023. Its authors call for more and larger studies before these findings can be relied on.
Dr. Kumar’s Take
L-theanine is popular as a calming supplement, and this review gathers the randomized trials in people with diagnosed mental disorders. The picture is more mixed than the marketing. The most striking results came from single trials in depression and OCD, where L-theanine was given together with an antidepressant (sertraline or fluvoxamine). Those numbers are large, but each rests on one study of about 50 people. The one trial in generalized anxiety disorder found it did no better than placebo for anxiety. It did help sleep satisfaction.
My read is that L-theanine looks safe and may help as an add-on in some conditions. It is not a proven stand-alone treatment for anxiety or depression, and it should not replace a medication that is working.
Study Snapshot
This systematic review included only randomized controlled trials of L-theanine in people diagnosed with a mental disorder. The authors searched PubMed, Scopus, PsycINFO, Web of Science, CINAHL Complete, and Cochrane up to June 2023. They screened 419 records and included 11 trials. They rated study quality with the Cochrane risk of bias tool. Nine trials had low risk of bias and two had some concerns, both due to missing data. The review describes each trial on its own rather than pooling them into one overall number.
Results in Real Numbers
The 11 trials came from six countries: Israel, Iran, the USA, Japan, Australia, and Italy. The review reports 827 participants receiving L-theanine. Participants’ average ages ranged from about 9 to 45 years. Four trials studied schizophrenia or schizoaffective disorder, two studied ADHD, and one each studied OCD, major depression, sleep problems, generalized anxiety disorder, and Tourette syndrome. Most trials lasted 8 weeks. The shortest lasted one day.
Major depression. In a 6-week trial, 60 patients on sertraline were randomly given L-theanine 200 mg a day or placebo. Fifty finished. Remission came in 68% of the L-theanine group versus 32% of the placebo group. Response came in 100% versus 84%. The number needed to treat for remission was 2.8, meaning that for roughly every 3 people given L-theanine instead of placebo, one more reached remission. Depression scores were lower in the L-theanine group at weeks 4 and 6.
OCD. In a 10-week trial, 50 adults on fluvoxamine were randomly given L-theanine (100 mg twice a day) or placebo. 92% of the L-theanine group had a complete response versus 36% of the placebo group. Obsession scores improved more with L-theanine, by about 5 points on the obsession scale at week 10. Compulsion scores did not differ.
Schizophrenia. All four trials used 400 mg a day added to antipsychotic drugs. One trial found lower anxiety, positive symptom, and general psychopathology scores, with effects seen from week 2. Another found lower negative symptom and general psychopathology scores. A third, which combined L-theanine with pregnenolone, found better negative symptoms, anxiety, and functioning.
ADHD. In a trial of 93 boys, L-theanine improved sleep efficiency measured by a wrist activity monitor. A small one-day crossover trial of 5 boys found L-theanine alone helped a cognition score but tended to worsen inhibitory control. The combination with caffeine looked better on both.
Generalized anxiety disorder. In an 8-week trial, 450 mg a day did not reduce anxiety more than placebo. It did improve sleep satisfaction.
Sleep problems and Tourette syndrome. In the sleep trial, L-theanine did not differ from placebo. In the Tourette trial, L-theanine with vitamin B6 reduced tic severity compared with psychoeducation, but not anxiety.
Side effects. No serious adverse events were reported. Some trials noted nausea, abdominal pain, headache, irritability, diarrhea, or constipation, at rates similar to placebo in the depression trial.
Who Benefits Most
The best results in this review came from people who took L-theanine together with a psychiatric medication. That includes adults with major depression on sertraline, adults with OCD on fluvoxamine, and people with schizophrenia on antipsychotics. Each of those findings comes from a small number of short trials.
People with generalized anxiety disorder are the group many would expect to benefit most. The one trial in that group found no extra benefit for anxiety over placebo, though sleep satisfaction improved.
Safety, Limits, and Caveats
L-theanine was generally well tolerated across the trials, with no serious side effects reported. The review lists its own limits: few studies, different populations and outcome measures, no standard dose, and possible publication bias. Most trials were small and lasted 10 weeks or less.
The review also notes rare reports of liver injury linked to green tea, mostly in people who drank excessive amounts for long periods. The quality of supplements can vary between brands.
Practical Takeaways
- The strongest results came when L-theanine was added to a standard medication, not used alone
- Most trials used 200 to 450 mg a day, split into two doses in several of them
- For generalized anxiety disorder, the one trial found no benefit for anxiety over placebo
- Side effects were mild and uncommon in these trials
- Do not stop or change a psychiatric medication on your own; talk with your doctor before adding a supplement
What This Means for Mental Health Treatment
This is the first systematic review of randomized trials of L-theanine across mental disorders. It suggests a possible role as an add-on treatment in some conditions, especially schizophrenia, anxiety disorders, and ADHD. The authors stress that the evidence is limited and that larger, better-designed trials are needed before L-theanine can be recommended with confidence.
Related Studies and Research
Episode 31: Depression Explained, The Biology Behind the Darkness
Episode 32: Depression Recovery Roadmap: A Step-by-Step, Evidence-Based Plan
FAQs
How quickly does L-theanine work for anxiety?
The trials in this review were short, from one day to 10 weeks. In one schizophrenia trial, lower anxiety scores appeared by week 2. In the depression trial, the L-theanine group pulled ahead by week 4. In the one generalized anxiety disorder trial, L-theanine did not beat placebo for anxiety.
Can I take L-theanine with caffeine?
One small one-day trial in 5 boys with ADHD found the combination of L-theanine and caffeine showed potential to improve cognition and inhibitory control. The review also notes that a 200 mL cup of tea contains about 25 to 60 mg of L-theanine. Check with your doctor if you take other medications.
What’s the optimal dose of L-theanine for mental health benefits?
Doses across the included trials ranged from 2.5 mg per kilogram of body weight up to 450 mg a day. The one generalized anxiety disorder trial in the review used 450 mg a day, given as 225 mg twice daily.
Bottom Line
A systematic review of 11 randomized trials found that L-theanine, mostly added to standard medication, reduced symptoms in schizophrenia, ADHD, depression, and OCD, and was well tolerated. The evidence is thin, with one or a few small trials per condition, and the one trial in generalized anxiety disorder found no benefit for anxiety over placebo.
