Doctor's Best Suntheanine L-Theanine 150mg Capsules 90

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  • Promotes a relaxed state without drowsiness.
  • Eases stress and everyday nervous tension.
  • Promotes a positive mood and alertness.

Doctor's Best Suntheanine® is the premier, patented form of the amino acid L-theanine. Suntheanine® is the purest form of the L-theanine on the market today. L-theanine is an amino acid derived from green tea that is responsible for the relaxation-inducing effect of team consumption.

Suntheanine® has been shown to promote an alert state of relaxation. This is characterized by an increase in alpha brain waves (signifying a relaxed, alert state) and a decrease in beta brain waves (signifying an awake, excited state of mind). Suntheanine® may also improve sleep quality, enhance mental acuity and soothe away tension and nervousness.


Active ingredient per capsule:
Suntheanine® L-theanine          150mg

Other Ingredients: Rice powder, modified cellulose (vegetarian capsule).


Adults - Take 1 capsule daily away from food, or as directed by your healthcare professional. 

Is Suntheanine safe for children?

L-theanine is a naturally occurring molecule that is present in the diets of children around the world where tea is a consumed and no concerns have ever been raised about its safety. Suntheanine, which is a purified form of the same amino acid found in green tea, has also been approved as a food ingredient and nutritional supplement in some countries for many years and in these countries it has a perfect safety record. There was a large double blind study recently done, in which 200mg of Suntheanine was consumed twice per day for six weeks in boys 8-12 years. No side effects were reported in any of these boys (Altern Med Rev 2011).

How much Suntheanine is too much?

Suntheanine can have noticeable benefits with doses as low as 50mg. However, for most adults, doses of 100mg to as much as 400mg or more are often used for greater effects. In doses of 400mg or greater, some people will experience some degree of drowsiness. This is advantageous if you are using Suntheanine to improve sleep quality, but it can be a problem during the day. Doses as high as 1000 mg of Suntheanine are safe but caution should be exercised if taking higher doses when you have to drive or operate machinery.


Promotes a relaxed state without drowsiness

Suntheanine® L-theanine is best known for its unique ability to promote relaxation without causing drowsiness. Evidence from animal studies sheds light on this seemingly counterintuitive effect of this unique tea-based amino acid. L-theanine administered to rats by IV in relatively higher doses following the administration of approximately the same dose of caffeine has been shown to blunt the stimulating effects of caffeine as assessed by EEG recordings. However, L-theanine administered in smaller doses on its own resulted in excitatory stimulation. This reported dual action of theanine was shown to be dependent on the dose administered 2. Additionally, there are many anecdotal reports of L-theanine simultaneously enhancing mental alertness, and some, though not all, preliminary research in humans confirms this. Previous studies showed that Suntheanine® L-theanine promotes alpha brain waves, traditionally interpreted as signifying a relaxed, alert state. In a randomized, placebo-controlled, crossover study comparing placebo, 50 mg and 200 mg L-theanine, the higher dose of L-theanine increased power in the alpha frequency band (8-13Hz) of the electroencephalogram across parietal and occipital areas of the brain relative to placebo. The alpha brain waves in the resting human volunteers were generated within 40 minutes after the oral administration of L-theanine (50–200 mg), signifying a state of relaxation without drowsiness, according to the study authors 3.

A study performed at the Brain and Cognition Laboratory at Oxford University investigated whether a lower dose of Suntheanine® L-theanine (50 mg) dissolved in tea would also affect alpha brain wave activity. The Suntheanine® group consisted of 16 participants who received 50 mg of Suntheanine® dissolved in a tea infusion, presumably containing caffeine. The control group consisted of 19 participants who received 100 mL cool water. EEG readings were taken 45 minutes after ingestion and subsequently every 15 minutes (45, 60,75, 90, 105 minutes). Participants were resting with their eyes closed during EEG recording. There was a greater increase in alpha activity across time in the Suntheanine® supplemented group relative to placebo (p<0.05) indicating that this lower dose of L-theanine may also have a significant effect on the feeling of relaxation 1.

May enhance cognitive performance and promote attention to detail

Studies have been performed in which L-theanine was administered to rats daily for four months to assess its effect on memory and learning ability. Several tests were employed to determine whether L-theanine could enhance memory and learning, including the Operant test in which food is released when the correct lever is pushed and a light comes on. L-theanine administration to rats resulted in a greater frequency of correct responses when compared to rats in the control group. In this experiment, the longer the L-theanine was administered, the better the response to the task. Additional tests performed on these animals included the passive and active avoidance tests. The idea here is that the animals develop the memory ability to avoid an undesirable outcome. The groups of animals receiving L-theanine again outperformed the control groups by exhibiting a greater ability to avoid undesirable events 3. These results demonstrate the memory and learning enhancement effects of L-theanine.

Furthermore, it seems clear that one of the mechanisms by which L-theanine supports cognitive health is through its potential antioxidant support for brain cells. Several laboratory investigations point to L-theanine’s ability to support the health of neurons in the face of induced oxidative stress. In one such experiment, cultured rat neurons were exposed to glutamic acid, resulting in significant cellular death. When these cells were simultaneously exposed to L-theanine, the cell death was suppressed 4. This antioxidant effect may yield a partial glimpse into Suntheanine®’s cognitive performance-enhancing actions.

Suntheanine® L-theanine clearly affects brain activity and is relatively fast acting; however, many of the mechanisms of how it supports cognitive health and brain performance in humans remain to be fully determined. More recent human clinical studies (2008) have discovered that the effects of L-theanine on alpha waves are likely both dose- and caffeine- dependent, as well as dependent on whether the user is in a resting state or actively performing an attention-demanding task. This emerging research indicates that when a large dose of L-theanine is ingested by itself or when it is ingested in combination with caffeine, L-theanine actually decreases background alpha activity, but promotes attention-related alpha brain wave processes during difficult attention-demanding tasks. This decrease in background alpha is associated with significant enhancement of one’s ability to actively perform tasks demanding a great deal of attention 6-8.

Another randomized, placebo-controlled, double blind crossover study published in 2008 also found differences between L-theanine alone and L-theanine with caffeine on relaxation and cognition. This study investigated the effects of L-theanine (250 mg), and caffeine (150 mg), in isolation and in combination, in 24 healthy volunteers who had abstained from caffeine for 12 hours 9. Results were measured 30 and 90 minutes after administration. At 30 minutes, L-theanine alone promoted the participants’ subjective ratings of “calm” and “relaxed” compared to baseline, while caffeine and L-theanine combined with caffeine both decreased these feelings.

However, the L-theanine/caffeine combination had significant positive effects on delayed word recognition reaction time. These results support the idea that the combination of L-theanine and caffeine may have beneficial effects on cognition and alertness, while L-theanine alone may promote relaxation 9. It therefore seems that L-theanine has differential effects based on whether it is administered alone or in combination with a stimulant such as caffeine and can be used either to enhance relaxation and calmness, or to enhance cognitive performance and alertness. 

Helps ease stress and everyday nervous tension

In one small investigation, eight Japanese female university students were selected as volunteers. Oral administration of 200 mg of L-theanine resulted in the generation of alpha brain waves in the occipital and parietal regions of the brains of the subjects when they were in a resting state, and resulted in a subjective feeling of relaxation. The intensity of alpha brain waves was significantly greater in the group of students with the highest levels of apprehension10.

In a double-blind study illustrating L-theanine’s anti-stress effects, it was found that a single dose influences both psychological and physiological states under acute stress. This study gave 12 participants a mental math task as an acute stressor. All participants underwent four separate trials: one in which they took L-theanine at the start of an experimental procedure, one in which they took L-theanine midway, and two control trials in which they either took a placebo or nothing. L-theanine intake resulted in lower levels of perceived stress during the math task, a significantly greater reduction in perceived stress from baseline, and a reduction in the heart rate and salivary immunoglobulin A (a biomarker of stress) responses to the acute stress task relative to the placebo. By analyzing the heart rate variability, the researchers found that the reductions in these acute stress responses were likely attributable to the significantly decreased activation of the sympathetic nervous system11.

Another study investigating the anti-stress effects of L-theanine found that a single dose was able to promote subjective feelings of tranquility in patients before the onset of acute nervous tension. The study also investigated the effect of L-theanine supplementation that followed the onset of apprehension and found that it did not induce relaxing behavioral effects. In this double-blind study consisting of 16 subjects, the researchers obtained behavioral measures of worry in all participants, both before and after an acute, experimentally created state of unease. L-theanine was able to promote ‘tranquil’ ratings, as measured on a visual analogue scale in rested participants. However, when participants were under conditions of increased acute apprehension, L-theanine did not have similar effects. In comparison, the placebo did not induce any relaxing effects at the initial measurement nor after the heightened state was induced 12. It seems L-theanine is an agent that is best used as a countermeasure to potential situations of nervousness and tension by supporting mental tranquility. Suntheanine® may normalize the body’s stress response and condition the body to handle stressful situations better.

Scientific References

  1. Nobre AC, Rao A, Owen GN. Asia Pac J Clin Nutr 2008;17 Suppl 1:167-8.
  2. Anonymous. Alternative Medicine Review 2005;10:136-137.
  3. Juneja L, Chu D, Okubo T, others. Trends Food Sci Tech 1999;10:199-204.
  4. Eschenauer G, Sweet BV. Am J Health Syst Pharm 2006;63:26, 28-30.
  5. Egashira N, Ishigami N, Pu F, others. Phytother Res 2008;22:65-8.
  6. Gomez-Ramirez M, Higgins BA, Rycroft JA, others. Clin Neuropharmacol 2007;30:25-38.
  7. Gomez-Ramirez M, Kelly SP, Montesi JL, Foxe JJ. Brain Topogr 2008.
  8. Kelly SP, Gomez-Ramirez M, Montesi JL, Foxe JJ. J Nutr 2008;138:1572S-1577S.
  9. Haskell CF, Kennedy DO, Milne AL, others. Biol Psychol 2008;77:113-22.
  10. Kobayashi K, Nagato Y, Aoi N, others. J Agri Chem Soc Japan 1998;72:153-157.
  11. Kimura K, Ozeki M, Juneja LR, Ohira H. Biol Psychol 2007;74:39-45.
  12. Lu K, Gray MA, Oliver C, others. Hum Psychopharmacol 2004;19:457-65.
  13. NutriScience Innovations L. 2000.
  14. Borzelleca JF, Peters D, Hall W. Food Chem Toxicol 2006;44:1158-1166.

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