Other names L-Theanine, N5-ethyl-L-glutamine, D-Theanine
Theanine is a naturally present amino acid found in Green Tea and Black Tea and is used by many people for its purported focus-boosting, stress-reducing, and mood-lifting effects. But is it effective for these purposes? Read on to find out what the science says.
This nootropic has no healthy human placebo-controlled studies that meet our inclusion criteria. Negative side effects can occur if used carelessly, so make sure you’re aware of the risks of Theanine.
Read about the effects of Theanine in relation to the amount of evidence we've found
Cognitive benefits of Theanine
One study found that Theanine enhanced both visual and auditory attention performance and reduced (which means improved) reaction times in healthy humans with high propensity to anxiety, but not in people with low propensity to anxiety.  This suggests that it might be useful for protecting cognitive functions under high-stress or high-anxiety circumstances, but that it doesn't enhance cognitive functions from a healthy baseline. Put in another way, by the authors of the study:
"... 200 mg of l-theanine intake may help normal people with high anxiety propensity to concentrate on their daily activities." 
In another study, Theanine did not prevent increases in anxiety.  This suggests it may only be effective for some people, or that it may only be effective in certain circumstances. However, there has also been one more study supporting its efficacy as an anxiolytic for people without anxiety disorders. 
When Theanine was given to healthy humans in 50mg doses, it had no acute beneficial effects on cognition or mood, suggesting this dose is too small.  On the other hand, 250mg Theanine impaired performance on a task requiring focus and memory performance in another study which examined its effects in healthy humans, so that dose may be too large.
To assess the effects of Theanine on stress and cognitive functions scientists gave 30 people the nootropic in 200mg doses daily for 4 weeks, in a study that examined its effects in healthy humans. After the end of the 4 week study period, participants had improved executive functioning scores and improved verbal fluency performance when they had taken Theanine for 4 weeks compared with when they had taken placebo for 4 weeks. Theanine was extra effective for cognitive enhancement in people with relatively poor baseline performance. 
Theanine for stress reduction
The effects of Theanine on stress in healthy humans have been examined in several studies.
In one study, 12 participants were given placebo, nothing, Theanine at the start of an experimental procedure, or Theanine in the middle of the experimental procedure.  In the experimental procedure, participants completed a stress-inducing task. After this procedure, participants who had taken Theanine had lower heart rate and increased heart rate variability, indicating anti-stress effects through attenuation of sympathetic nervous activation, according to the study authors.
Another study examined the effects of Theanine on relaxation and anticipatory anxiety in healthy humans.  It was found that Theanine increased subjective relaxation levels during rest, but that it did not prevent increases in anxiety in a situation designed to cause anxiety.
Theanine improved several stress-related measures in healthy people after 4 weeks of use in 200mg doses daily. 
Theanine for improved sleep
It also improved sleep in boys with ADHD when used in 200mg doses with breakfast and in the afternoon (200mgX2/day). 
The legality and side effects of Theanine
Frequently asked questions about Theanine
Studies conducted on the effects of Theanine in healthy humans
Last updated Saturday, June 10, 2023