July 31, 2025, 2:04 am | Read time: 6 minutes
The amino acid L-theanine is said to enhance concentration, calm the mind, and even improve sleep without causing drowsiness. Additionally, it is believed to work well with caffeine. But isn’t all of this contradictory? FITBOOK explains what this substance is all about and where it can be found.
What Is L-Theanine?
A natural compound that promises increased mental performance while keeping you relaxed—and all without side effects? What sounds like the perfect remedy for our sometimes hectic lives actually exists: L-theanine. This amino acid is primarily found in true tea (Camellia sinensis), with green tea having a slightly higher content than black tea. However, the dose is often so low that you hardly notice any effect.1
High-quality green tea, especially the matcha variety, contains a lot of L-theanine. The reason: The tea plants are shaded in the weeks leading up to harvest. This natural process significantly increases the formation of this amino acid in the leaves.
But for those who don’t want to drink several cups of tea regularly, dietary supplements are often the go-to today. In Japan, L-theanine was approved as a stress-reducing agent back in the 1990s.2 It is now widespread globally and a staple in many functional products, from capsules to powders to fortified drinks.
The Effects of L-Theanine
L-Theanine Alone Has a Calming Effect
A study from the University of Shizuoka in Japan showed as early as 1999 that L-theanine stimulates the so-called alpha waves in the brain.3 This promotes relaxation without causing drowsiness. The researchers concluded that L-theanine, and thus the consumption of green tea, leads to stress reduction. They also reported earlier animal studies on rats that showed L-theanine positively affected the animals’ learning performance and memory. Another study from Japan in 2006 confirmed the relaxing or calming effect of L-theanine on humans.4 Experiments with rats also showed that the substance has a blood pressure-lowering effect.5
An extensive study from Japan confirms further positive properties of the compound. In a four-week trial, healthy adults received 200 milligrams of L-theanine daily as a supplement. After four weeks, participants reported a significant decrease in stress-related complaints. Both depressive moods and persistent inner tension decreased significantly. At the same time, sleep quality improved—falling asleep was easier, nighttime disturbances decreased, and the use of sleeping pills became less frequent. And all these effects occurred without side effects like fatigue at undesirable times of the day.6
L-Theanine Combined with Caffeine—Gently Energizing and Performance-Enhancing
A Turkish study examined how the effects of single and combined caffeine and L-theanine supplementation manifest. The shooting ability and cognitive performance of elite curling athletes were tested. They received either caffeine (6 mg/kg), L-theanine (6 mg/kg), or both together to test concentration and accuracy in curling. The athletes performed best after the combined intake of the two compounds, both in cognitive tests and precise throwing tasks. The combination led to faster reaction times, fewer errors, and a significantly better hit rate. The individual doses also had positive effects, but not as pronounced.7
The study authors suspect that the stimulating effect of caffeine and the balancing effect of L-theanine complement each other ideally. The result: alert and focused, but without nervousness or jitters.
The L-theanine in tea acts somewhat like a counterbalance to caffeine. Caffeine not only wakes you up but also has unpleasant side effects. Especially in higher doses, it can lead to heart palpitations, inner restlessness, insomnia, and increased blood pressure. This is where L-theanine comes into play, as it is said to neutralize the negative effects of caffeine. What results is the often-described effect of green tea: it gently wakes you up—not as stimulating as coffee, but longer-lasting—and relaxes you at the same time. As the Turkish study shows, this is a promising effect that can also be interesting for athletes.
The Right Dosage
L-theanine is available in Germany and the EU as a dietary supplement in capsule or powder form. According to EU data, the substance is well-characterized and meets legal requirements. A daily dose of 200 milligrams is considered safe.8 Even if you have concerns about falling asleep, you can rest assured. A systematic review of eleven clinical studies on the effects of L-theanine on sleep shows the following: The authors report significant improvements in various sleep parameters, such as sleep onset time, total sleep time, sleep quality, and morning recovery. However, it is also crucial to note that doses over 655 milligrams daily not only offer no further benefits but could potentially be detrimental to sleep quality.9
The Use and Effect of Hojicha Tea
Ingredients and Effects of Black Tea
Federal Institute for Risk Assessment on the Use of L-Theanine in Beverages
Although L-theanine in naturally occurring amounts, such as in tea, is considered harmless, the Federal Institute for Risk Assessment (BfR) sees the risk of negative effects on reaction time and attention at very high artificially added doses as not sufficiently clarified. Therefore, the use of artificially added L-theanine in beverages is not allowed in Germany.
“Due to the fact that too little is known about the desired and undesired effects of isolated L-theanine in the human body, the BfR rejects the addition of isolated L-theanine in beverages,” according to an assessment from 2003.10 This assessment remains the current position of the BfR.
But is the use of L-theanine in beverages now banned? The clear answer is: No! L-theanine can be used in beverages, provided it meets certain guidelines:
- L-theanine must not be used as a coloring agent, preservative, or emulsifier.
- No unauthorized health claims may be made.
- The amount must be toxicologically safe.
- There must be correct labeling; the label must clearly and honestly state where the substance comes from.
The Assessment of U.S. Authorities
The U.S. Food and Drug Administration (FDA) has a few concerns and already awarded L-theanine the designation “generally recognized as safe” in 2007.
According to its study evaluation, the FDA assumes that 250 milligrams of L-theanine per serving in beverages and foods can be consumed without concern. This corresponds roughly to what a regular tea drinker consumes per day. According to the FDA, a heavy tea drinker consumes up to 825 milligrams of L-theanine per day. Thus, this amount is also considered safe.
However, you can generally skip powders or capsules with the compound: If you want to relax while staying mentally sharp, you can simply drink more black and green tea. They also bring many other valuable ingredients, such as antioxidants.