Neurotransmitter findings depend on the model
Reviews discuss effects involving glutamate, GABA, dopamine and serotonin. One reviewed animal combination experiment reported reduced serotonin rather than a simple increase. Species, brain region, dose and coingredients affect what such findings mean. [1][2]
Human outcomes do not reveal one chemical mechanism
A change in attention, stress score or brain-wave activity is not a direct measurement of brain serotonin. Human trials do not establish that a person feels calmer because a serotonin deficiency was corrected. [2]
Clinical mood evidence remains limited
A recent meta-analysis found mixed anxiety findings and called for confirmation of possible mood effects. Those data do not establish theanine as an antidepressant replacement or a predictable way to manipulate a neurotransmitter. [3]
Do not build a combination from a serotonin claim
Imagine someone taking an antidepressant adds a product labeled serotonin support. Review the actual ingredients and medicines with the prescriber. Do not infer compatibility, deficiency or a need to alter treatment from a marketing description. [4][5]
| Finding | Not established |
|---|---|
| Animal neurotransmitter change | Same human direction |
| Relaxed feeling | Corrected deficiency |
| Alpha-wave change | Serotonin measurement |
| Mood signal | Replacement for prescribed care |
Sources for this article
- Frontiers | L-Theanine: A Unique Functional Amino Acid in Tea (Camellia sinensis L.) With Multiple Health Benefits and Food Applications
Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product. - Frontiers | Effects of L-theanine on cognition, mood and sleep: evidence from human trials
Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product. - Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials.
Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product. - Dietary Supplements: What You Need to Know
Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product. - L-Theanine | Memorial Sloan Kettering Cancer Center
Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.