A Complete Guide to L-Theanine

A Complete Guide to L-Theanine

L-theanine is a special amino acid commonly found in tea leaves (Camellia sinesis) and certain functional fungi. It's a common ingredient in supplements. Current research indicates that L-theanine can soothe anxiety, promote relaxation, and boost cognitive function. 

Tonicc contains 200 mg per serving (~5 mL), usually added to your morning hot beverage. Pairing L-theanine and caffeine appears to produce synergistic effects, further bolstering your focus and mental clarity while reducing the caffeine jitters.

Read on to learn more about L-theanine's benefits, uses, safety, and more. 

In this guide:

  • What is L-Theanine?
  • L-Theanine Uses and Benefits
  • How It Works
  • L-Theanine and Caffeine
  • Dosages, Safety, and Known Interactions

What is L-Theanine?

Discovered in 1949, L-theanine (or L-gamma-glutamylethylamine) is an amino acid analogue found primarily in plants and fungi. Tea leaves, in particular green tea, are the most common dietary source. It's thought to influence the levels of certain chemicals in the brain, including the neurotransmitters serotonin and dopamine, which are critical for mood, sleep, and emotional regulation. 

L-Theanine Uses and Benefits

Primarily used to help people relax and increase their focus, L-theanine's benefits are responsible for many of the soothing effects of tea. 

Anti-Anxiety and Stress Reduction

Consuming L-theanine helps fortify your mind and body against stress. It's what's known as an adaptogen. 

According to one study, people who consume L-theanine experience a reduction in heart rate and salivary immunoglobulin A (s-IgA). Together, these responses indicate a reduction in the psychological and physiological stress response. The mechanism is likely the attenuation of sympathetic nervous activation – the cause of the 'fight or flight response.' 

Furthermore, a 2016 systematic review confirmed these findings. Of the five randomized control trials (RCTs) identified, four demonstrated a significant reduction in stress and anxiety. Another review of L-theanine and green tea consumption reports that 200-400 mg per day assisted in the reduction of stress and anxiety in people experiencing stressful conditions. 

Enhanced Focus

L-theanine is believed to boost focus and attention. In an RCT involving 30 people, L-theanine (200 mg/day) taken for four weeks caused significant increases in verbal fluency and executive function compared to placebo. Moreover, the supplement reduced sleep latency, disturbance, and sleep medication usage, indicating a potential underlying mechanism. As the authors concluded, L-theanine has the "potential to promote mental health in the general population." 

Several studies have noted the combined effect of L-theanine and caffeine on cognitive performance and subjective alertness. In particular, research has highlighted the ameliorative effect of L-theanine on caffeine-related jitters. See below for further details.

Immune Support

Another health benefit of L-theanine is its immunomodulatory effects. One 2016 study claimed that consumption of tea is linked to a reduction in upper respiratory infections. It's a potential explanation for why tea is traditionally given to people feeling unwell.

A 2011 study posits a combined effect of L-theanine and green tea catechins (antioxidants). Together, these compounds appeared to reduce the risk of an influenza infection among healthcare workers. It could form a prophylactic treatment.

On the other hand, another analysis found that L-theanine can relieve intestinal stress and reduce inflammation. However, the study was conducted on rats, so it may not be applicable to human populations.

Blood Pressure Management

Aside from its psychological effects, L-theanine also reduces the physiological responses to stress. Blood pressure often spikes in response to stressful situations. Prolonged high blood pressure (hypertension) is a risk factor for stroke, heart disease, and several other conditions.

A 2012 analysis found that L-theanine-inhibited blood pressure increases in people who usually experience a significant spike in blood pressure. Compared to caffeine, L-theanine produced a greater reduction, which mirrored its anti-anxiety effects.

How It Works

L-theanine primarily influences neurotransmitter activity in the brain, altering the central nervous system's (CNS) regulation of stress and anxiety. Unlike other compounds, L-theanine is highly effective at crossing the blood-brain barrier: a selective permeability barrier separating the brain from the general blood circulation.

Once in the brain, L-theanine boosts the production of gamma-aminobutyric acid (GABA). This neurotransmitter is responsible for down regulating neuronal excitability. So, with less random firing, your anxiety levels plummet, promoting a sense of relaxation. 

The same mechanism could also explain the increased focus. With less neuronal excitability, the brain finds it easier to concentrate on a particular task without becoming distracted. That's why L-theanine is a popular supplement in people with attention deficit hyperactivity disorder (ADHD).  

In addition, L-theanine modulates levels of other key neurotransmitters, such as dopamine and serotonin. Balancing these neurotransmitters boosts mood and cognitive function, further contributing to mental clarity and focus. This effect is compounded when L-theanine is consumed with caffeine. 

Finally, there's growing evidence for L-theanine's effects on alpha brain waves. In a 2003 study, adult males who consumed 200 mg of L-theanine saw greater release of alpha waves related to mental relaxation and concentration. Exactly how they achieve this effect requires further study. 

L-Theanine and Caffeine

L-theanine and caffeine act synergistically to enhance each other's effect and ameliorate some negative side effects. The primary result is a boost in attention and concentration. 

What's the evidence? A 2008 study examined the effect of L-theanine and caffeine in young adults performing cognitively demanding tasks. Paired together, the compounds improved accuracy and self-reported alertness and reduced self-reported tiredness. Participants consumed 100 mg of L-theanine and 50 mg of caffeine. 

In a 2010 study, 44 young adults received either a mix of 97 mg of L-theanine and 40 mg of caffeine or a placebo. Researchers monitored several parameters, including cognitive performance, alertness, blood pressure, and heart rate. Those who received the combination treatment experienced notably improved accuracy during tasks that required switching attention and also reported increased alertness.  

Dosages, Safety, and Known Interactions


As a supplement, L-theanine is available in capsules, gummies, liquids, soft gels, tablets, and powders. Tonicc contains a liquid form of L-theanine that will seamlessly blend in any drink. 

Current research usually advises a 200 mg dosage of L-theanine per day. However, many studies range from just 100 mg to 400 mg. In fact, consuming 400 mg per day produced the highest results in auditory processing – a form of cognitive function. Meanwhile, doses as low as 50 mg can increase relaxation

If you're using Tonicc, we advise beginning with a half-serving (½ pump or 2.5 mL). You can then monitor your feelings over several days to see if you notice an effect. Increase the dosage up to 1 pump daily until you feel you're getting the maximum benefit. 


L-theanine is well-tolerated in most clinical trials. However, adverse effects are still possible. Some people are allergic or hypersensitive to L-theanine or tea. Always read product labels carefully and seek immediate medical attention if you have breathing difficulties or other symptoms of a severe allergic reaction.

Women who are pregnant or breastfeeding should avoid L-theanine supplements. However, some tea is still okay to drink. 

Medication Interactions

L-theanine is generally safe with most other supplements and prescribed medications. Speak to your healthcare provider or pharmacist for an in-depth medication review related to L-theanine. Potential drug interactions include:

  • Anxiety Medication. Because theanine alters the brain to reduce anxiety, it may interact with similar medications. 
  • Blood Pressure Medication. Blood pressure medication, or antihypertensives, may further reduce blood pressure in people taking L-theanine. Rather than being beneficial, a person's blood pressure may drop too low. This increases the risk of postural hypotension (a drop in blood pressure when standing). 
  • Sedative Medication. L-theanine may cause sleepiness and slowed breathing. Sedatives, or CNS depressants, have a similar mechanism of effect. Use L-theanine with caution if you're taking sedative medications.
  • Cancer Medication. Never take L-theanine alongside chemotherapy unless you've spoken to your healthcare provider. 

Key Takeaways

  • L-theanine is a naturally occurring amino acid found in tea leaves, especially green tea, and certain fungi. It is renowned for its calming effects on the brain, enhancing relaxation and cognitive function without causing drowsiness.
  • L-theanine increases the production of calming neurotransmitters like GABA, serotonin, and dopamine, which help improve mood and enhance mental focus, contributing to a state of relaxed alertness.
  • Regular consumption of L-theanine significantly reduces physiological stress markers such as heart rate and salivary immunoglobulin A, aiding in relaxation and reducing anxiety levels effectively.
  • L-theanine, when combined with caffeine, improves alertness, focus, and accuracy during cognitive tasks while also reducing the adverse effects of caffeine, like jitteriness.
  • Beyond mental health, L-theanine has immunomodulatory effects, potentially reducing the incidence of upper respiratory infections and supporting overall immune function.
  • L-theanine is generally well-tolerated with minimal side effects. Effective daily doses range from 100 mg to 400 mg, but it's essential to be mindful of potential interactions with medications, particularly those for blood pressure and anxiety. Consult your physician or pharmacist to ensure L-theanine or Daily Vitality do not have negative interactions with your medications or medical conditions.