l-theanine vs gaba — what is the difference?

gaba: the neurotransmitter, and the catch

gaba is gamma-aminobutyric acid, the main inhibitory neurotransmitter in the human brain. your body already makes it. the appeal of a gaba supplement is obvious — take the calming molecule directly.

the catch is the blood-brain barrier. whether oral gaba crosses it in meaningful amounts is genuinely unsettled, and researchers say so in print. a 2018 randomized double-blind study of oral gaba on visual attention states in its own abstract that there is controversy about whether oral gaba can cross the barrier, while still reporting an effect on one of its measures.

so the fair position is: contested, with some human results, and not something anyone should present as settled.

l-theanine: less famous, better evidenced

l-theanine is an amino acid found naturally in green tea leaves. the important structural difference is that it does cross the blood-brain barrier — lardner (2014) reviews the neurobiology — which is exactly the step oral gaba is disputed on.

the human evidence is also deeper. kimura and colleagues (2007) recorded reduced psychological and physiological stress responses during an acute task. white and colleagues (2016) ran a double-blind crossover trial with magnetoencephalography alongside subjective measures. hidese and colleagues (2019) ran four weeks of daily dosing in healthy adults and measured both stress-related symptoms and cognitive function.

williams and colleagues (2020) reviewed the field systematically; payne and colleagues (2025) reviewed it again across cognition, sleep and mood. that is several independent research groups over nearly two decades, which is not something the oral-gaba literature can match.

it is also studied for what researchers describe as alert relaxation — calm without sedation — which is why it appears in products meant for daytime use rather than bedtime ones.

reading the two literatures side by side

deshpande and colleagues (2025) is the most directly useful paper here: a randomised controlled study putting both amino acids in the SAME protocol, in preoperative patients, measuring sedation, anxiety and cognition. having them compared under one design removes most of the usual apples-to-oranges problem.

for gaba on its own, the positive work exists but comes with conditions attached. guimarães and colleagues (2024) reported improved heart-rate variability and sleep efficiency — in sedentary, overweight men undergoing physical exercise, a population that is not most people reading this. leonte and colleagues (2018) found an effect on one temporal-attention measure and none on spatial attention, while flagging the barrier question in the same abstract.

notice what is missing on the gaba side: no large systematic review finding consistent effects in healthy adults, and no settled account of how it would work. that absence is the answer to the question in the title.

so why do products pair them?

three reasons, and only one is scientific. they are believed to act on the same inhibitory system from different angles. gaba is the name customers recognise on a label. and formulating with both is cheap.

nula uses l-theanine 100mg and gaba 50mg per serving — the better-evidenced ingredient at double the dose of the contested one. that ratio is a deliberate statement about which literature we think holds up, and it is the ratio to look for on any label that lists both.

if a product leads with gaba and leaves l-theanine as the afterthought, or hides both inside a proprietary blend so you cannot see the split at all, that tells you something.

common follow-ups

sources

1. Deshpande and colleagues (2025). Comparison of the effects of two amino acids, Gamma-aminobutyric acid (GABA) and L-theanine, on sedation, anxiety, and cognition in preoperative surgical patients - A randomized controlled study. Journal of Anaesthesiology, Clinical Pharmacology.
2. Leonte and colleagues (2018). Supplementation of gamma-aminobutyric acid (GABA) affects temporal, but not spatial visual attention. Brain and Cognition.
3. Guimarães and colleagues (2024). GABA Supplementation, Increased Heart-Rate Variability, Emotional Response, Sleep Efficiency and Reduced Depression in Sedentary Overweight Men Undergoing Physical Exercise. Journal of Dietary Supplements.
4. Kimura and colleagues (2007). L-Theanine reduces psychological and physiological stress responses. Biological Psychology.
5. White and colleagues (2016). Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover Trial. Nutrients.
6. Hidese and colleagues (2019). Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients.
7. Williams and colleagues (2020). The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review. Plant Foods for Human Nutrition.
8. Payne and colleagues (2025). Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood. Nutrition Reviews.
9. Lardner (2014). Neurobiological effects of the green tea constituent theanine and its potential role in the treatment of psychiatric and neurodegenerative disorders. Nutritional Neuroscience.
10. Nawarathna and colleagues (2025). High-dose L-theanine-caffeine combination improves neurobehavioural and neurophysiological measures of selective attention in acute stress. The British Journal of Nutrition.

These references describe research on the ingredients, not on Nula Calm Gum. Last reviewed August 17, 2026.