Functional amino acids for relaxation: GABA, glycine and L-theanine

By Kelly C. Heim, Ph.D.

According to the National Health Interview Survey, 75% of the general population experiences some form of stress at least every two weeks.1 The American Psychological Association asserts that lifestyle and dietary approaches to relaxation may support not only emotional well-being, but cardiovascular, immune and metabolic health.2 The ability of the brain and body to relax depends on proper neurotransmission—the communication between neurons in the central nervous system (CNS).

Supporting inhibitory neurotransmission: GABA and glycine

There are two basic types of neurotransmission—inhibitory and excitatory. Shifting the balance in favor of inhibitory signals is essential for relaxation. GABA (gamma aminobutyric acid) is the principal inhibitory neurotransmitter in the CNS. This unique amino acid works by binding to GABA receptors in the membranes of neuronal junctions, or synapses (Figure 1). Once bound, the receptor opens to allow negatively charged chloride ions to flow into the cell. The negative charge on the inside of the membrane and the positive charge on the outside limits the neuron’s ability to respond to further stimulation.

Figure 1. Inhibitory neurotransmission. GABA and glycine are released from a presynaptic neuron (blue), then cross the synapse to bind to receptors on another neuron (or postsynaptic neuron, green). Receptor binding causes chloride ions to exit the cell. This renders the neuron less capable of responding to stimulating signals.

Whether orally administered GABA can cross the blood-brain barrier to access CNS neurons has been a salient point of controversy in recent years. However, the efficacy of orally administrated GABA has been established in human clinical research in which brain waves are assessed by electroencephalograms (EEG). This method measures the magnitude of different types of brain waves. Beta waves reflect a high level of alertness and wakefulness, while alpha waves typify a calm, lucid form of relaxation. In a placebo-controlled study, a GABA supplement modulated beta wave activity while significantly promoting alpha wave activity within 1 hour following a single oral dose.3

Like GABA, glycine is a principal inhibitory amino acid neurotransmitter that binds to chloride ion channels to relax CNS neurons. Oral administration of glycine prior to sleep has been shown to support general subjective and objective indices of sleep quality and moderate daytime fatigue.4,5 In addition, significant support for memory and overall cognitive performance has been reported in several studies.5,6

Taming excitatory neurotransmission: L-theanine

L-theanine, an amino acid found in green tea, exhibits a molecular structure nearly identical to glutamate, an excitatory neurotransmitter. While its molecular mechanisms await thorough delineation, scientists believe L-theanine’s structural nuance allows it to act as a “Trojan horse” at glutamate-responsive proteins and receptors.7 As such, it may compete with glutamate to balance its excitatory effects. Preclinical studies indicate that L-theanine also supports healthy levels of serotonin, dopamine, and GABA in the brain.7 In human clinical studies, L-theanine supports both objective and subjective indices of relaxation.

In a study of healthy, young participants, EEG measurements following a single dose of L-theanine revealed significant support for alpha activity within 1 hour relative to placebo.8 These findings corroborate a prior study of college-aged women, in which support for alpha wave formation in the occipital and parietal regions of the brain was significant in response to L-theanine supplementation.9

Pure Tranquility liquid delivers GABA, glycine and l-theanine in a great-tasting liquid. The gentle actions of these amino acids support relaxation without compromising cognitive performance. This convenient liquid may be taken regularly or on a periodic basis to help moderate occasional stress.


  1. Stress facts and statistics. National health interview survey. University of Maryland. USA;2009.
  2. American Psychological Association.
  3. Abdou AM, Higashiguchi S, Horie K, et al. Relaxation and immunity enhancement effects of gamma-aminobutyric acid (GABA) administration in humans. Biofactors. 2006;26(3):201-208.
  4. Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012;3:61.
  5. Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms 2007;5(2):126–131.
  6. File SE, Fluck E, Fernandes C. Beneficial effects of glycine (bioglycin) on memory and attention in young and middle-aged adults. J Clin Psychopharmacol. 1999;19(6):506-512.
  7. Nathan PJ, Lu K, Gray M, Oliver C. The neuropharmacology of L-theanine (N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. J Herb Pharmacother. 2006;6(2):21-30.
  8. Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-168.
  9. Kobayashi K, Nagato Y, Aoi N, Juneja LR, Kim M, Yamamoto T, Sugimoto S. Effects of L-theanine on the release of alpha-brain waves in human volunteers. Nippon Noegikagaku Kaishi 1998;72(2):153-157.

For educational purposes only. Consult your physician for any health problems.

*These statements have not been evaluated by the Food & Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.