What Happens to Your Brain Function When You Take L-Theanine Every Day

L-theanine, a component of green and black tea, may improve brain function- but there’s not enough data to know for sure. Most research on l-theanine’s effects on the brain comes from single-dose studies, not long-term use.

1. Brain Function May Be Enhanced

• Limited evidence from a few small studies suggests that taking l-theanine regularly may improve cognitive function.
• A study of 30 healthy adults showed that those who took 250 milligrams (mg) of l-theanine daily for four weeks could better express themselves verbally (they had higher verbal fluency). The group who supplemented with l-theanine also experienced a boost in complex thinking skills (executive function). In this study, the brain benefits of l-theanine were greater among people with lower baseline cognitive test scores.
• Another small study of 20 adults with major depressive disorder showed that taking 250 mg of l-theanine daily for 8 weeks improved recall of words (verbal memory), shortened the time to answer test questions, and reduced errors. Notably, this study was open-label, meaning participants knew they were taking the supplement. Given this and the small sample size, further research is needed to verify these results.
• A combination of l-theanine and green tea extract taken daily for 16 weeks improved memory in a study of 91 adults with mild cognitive impairment.

2. Attention May Be Improved

• You may be more alert and focused if you take l-theanine with caffeine.
• But while a one-time dose of l-theanine can boost attentiveness, regular use seems less likely to do so.
• A clinical trial showed that taking l-theanine daily for 12 weeks did not improve attention span in adults aged 50 to 70.

3. Stress May Be Reduced

• L-theanine may help you relax without making you drowsy, according to some research.
• Animal studies show that l-theanine increases levels of calming chemical messengers in the brain (neurotransmitters) such as serotonin, norepinephrine, and dopamine.
• A small study of 30 healthy adults showed that taking 200 mg per day of l-theanine for four weeks reduced anxiety symptoms.
• Supplementing with 250 mg of l-theanine daily for eight weeks was also shown to help manage anxiety symptoms in a small study of adults with depression. This was an open-label study, so more data is needed to confirm these effects.

How Much L-Theanine Should I Take?

• There is no specific dosage recommendation for l-theanine for brain health.
• Typical l-theanine supplement dosages range from 50 to 250 mg.
• It has been studied in clinical trials for brain function at dosages of 50 to 500 mg.
• To put this in perspective, a cup of green or black tea contains about 12-25 mg of l-theanine.
• Do not take more than 1200 mg of l-theanine daily. Side effects are rare, but high amounts of this supplement may cause headache, dizziness, and gastrointestinal issues.
• Discuss l-theanine or any dietary supplement with your healthcare provider before adding it to your medicine cabinet for personalized recommendations and optimal safety.