Can L-Theanine from Green Tea Help Treat Depression?

Can L-Theanine from Green Tea Help Treat Depression?

Possibly, as an add-on, but the evidence here is early. In this small open-label study from Japan, 20 adults with major depressive disorder added 250 mg of L-theanine a day to their current medication for 8 weeks. Their depression scores on the 21-item Hamilton Depression Rating Scale fell (p = 0.007), and anxiety, sleep and several measures of thinking also improved. There was no placebo group, so the study cannot show how much of that change came from L-theanine itself.

L-theanine is an amino acid found almost only in green tea (Camellia sinensis). It has been suggested to have a range of effects on mood and the brain, which is why the researchers tested it in people with depression.

Dr. Kumar’s Take

This is a pilot study, and it should be read as one. Twenty people, no control group, and everyone stayed on their existing medication. Depression scores often improve over 8 weeks for many reasons, including the extra attention of being in a study. The results are consistent and cover more than mood: anxiety, sleep and cognitive tests all moved in the right direction, and no safety problems came up. That makes L-theanine a reasonable candidate for a proper placebo-controlled trial, which is exactly what the authors call for. It does not make it a proven depression treatment.

Study Snapshot

• Participants: 20 adults with major depressive disorder (4 men, mean age 41; 16 women, mean age 43)
• Intervention: L-theanine 250 mg per day, added to each person’s current medication
• Duration: 8 weeks, with assessments at baseline, 4 weeks and 8 weeks
• Design: Open-label, no placebo group
• Measures: Hamilton Depression Rating Scale (HAMD-21), State-Trait Anxiety Inventory, Pittsburgh Sleep Quality Index, the Stroop test and the Brief Assessment of Cognition in Schizophrenia

Results in Real Numbers

• Depression: HAMD-21 scores fell after L-theanine (p = 0.007). The drop was seen in patients who were not in remission at baseline (HAMD-21 above 7; p = 0.004).
• Anxiety: Trait anxiety scores fell (p = 0.012).
• Sleep: Sleep quality scores improved in patients not in remission at baseline (p = 0.030).
• Thinking: On the Stroop test, response time (p = 0.001) and error rate (p = 0.036) both fell. Verbal memory (p = 0.005) and executive function (p = 0.016) improved.
• Safety: The authors conclude that 8 weeks of L-theanine was safe.

Safety, Limits, and Caveats

The open-label design is the main limit. Without a placebo group, the natural course of depression, the ongoing medication and the expectation of benefit can all explain some of the improvement. The sample was small, and all participants were already on treatment, so the results say nothing about L-theanine used alone. Some of the authors were from the research division of Taiyo Kagaku, a Japanese food ingredient company.

Practical Takeaways

• This study tested L-theanine as an add-on to existing depression treatment, not as a replacement.
• The dose studied was 250 mg per day for 8 weeks.
• The improvements in mood, anxiety, sleep and thinking are promising but unconfirmed until placebo-controlled trials are done.
• If you are being treated for depression, talk with your prescriber before adding any supplement.

Related Studies and Research

• L-Theanine Adjunct to Sertraline for Major Depression

• Episode 31: Depression Explained, The Biology Behind the Darkness

• Episode 32: Depression Recovery Roadmap: A Step-by-Step, Evidence-Based Plan

• Effects of L-Theanine Supplementation on Mental Disorders

FAQs

How much L-theanine was used in this study?

Participants took 250 mg per day for 8 weeks, on top of their usual medication.

Is L-theanine safe for long-term use in depression?

In this 8-week study the authors concluded it was safe. Longer-term safety in depression was not tested here.

Can L-theanine replace antidepressant medications?

No. Everyone in this study stayed on their existing medication, so it only speaks to L-theanine as an add-on. Work with your prescriber before changing any treatment.

Bottom Line

In 20 adults with major depression, adding 250 mg of L-theanine a day to their usual medication for 8 weeks was followed by lower depression, anxiety and sleep scores and better performance on memory and attention tests. Without a placebo group, these results are a starting point for controlled trials, not proof that L-theanine treats depression.

Read the study