Blog Post

L-Theanine: Is It Worth Taking?

L-Theanine Feature Image

L-Theanine is arguably an underrated tool when it comes to managing stress and anxiety. It is not an overly popular option amongst the general population, but it consistently appears to have benefits. There also appears to be minimal downside.

In this post, the research on L-Theanine will be discussed and we will explore whether it is worth taking.

What is L-Theanine

L-Theanine is an amino acid that is naturally found in certain plants. It is most consumed naturally in the form of tea.

A cup of tea

Although we naturally consume it through tea, the dosage in tea is usually below the optimal dosage for benefits. The content in tea varies, but it is usually <50mg, while the clinically relevant dosage that is often used in research finding benefits is >100mg.

Theoretically, the benefits of L-Theanine come from increased alpha-waves in the brain, which is associated with relaxation.


Improvements in stress and anxiety are the main benefits of L-Theanine. I will go through these separately to look at the research on each topic individually.

There are more studies than just those four, but some common themes are clear. Every study I am aware of L-Theanine that measures stress shows improvements. The dosages utilised consistently are around the 200mg mark as well.


Stress and anxiety are often grouped together when people talk about L-Theanine. The research on anxiety-related outcomes is not nearly as promising though.

A 10-week randomized controlled trial involving 450-900mg L-Theanine per day in those with anxiety did not find any advantages over placebo. It did however improve sleep outcomes.

Another study found that 200mg L-Theanine improved relaxation but did not reduce anxiety in experimentally induced anxiety situations.

A 2016 systematic review on the topic of stress and anxiety only found 5 relevant studies in humans that used 200-400mg of L-Theanine. Of those studies, only one involved participants with anxiety, which was the 10-week trial mentioned above.

The four studies that did not involve participants who had been diagnosed with anxiety found improvements in measures of anxiety.

Those improvements are worth being aware of. But it would be a stretch to say that there is good research to indicate that it can consistently help with anxiety.


Woman in deep sleep

L-Theanine does not directly improve sleep. In fact, that is part of its appeal. By helping with relaxation, without having a drowsiness effect, it could be helpful for those who want to perform well in stressful situations.

Although there is no direct effect, research consistently finds that L-Theanine improves sleep. This is likely due to the reductions in feelings of stress.

There is not a massive amount of research, but it looks consistently positive.

Based on the evidence, I would wager it is unlikely to help sleep in those with low stress levels. Considering the majority of people report stress being a factor that affects their sleep though, it makes sense that it consistently helps a large portion of people.

Combining L-Theanine and Caffeine

L-Theanine and caffeine are a common combination that is recommended for those wanting to improve productivity.

Caffeine has well-documented benefits for focus, productivity and cognitive function, amongst other things.

Alongside those benefits, there are some downsides. It can increase feelings of stress and anxiety, increase heart rate, and in some cases increase blood pressure too.

The combination of L-Theanine and caffeine has been shown to improve alertness and cognitive performance while minimising some of the negatives of caffeine.

Of course, L-Theanine does not offset all the other negatives of caffeine, such as the impact on sleep and absorption of certain nutrients.

Are There any Downsides or Side Effects?

L-theanine is one of the safest supplements we have access to.

We do not have a lot of long-term data using high dosages. But there are some studies that can give us confidence that it is unlikely to be an issue when used in normal amounts.

One study on rodents used 4,000mg of L-Theanine per kg of body weight per day for 13 weeks, and found no issues. That is an insanely high dosage, so it is reassuring that even with that there were no issues.

There are no common side effects that are reported. Of course, it is always worth double-checking with your doctor, particularly if you are on medications, to see if there are any potential interactions.

Dosage and How to Take

L-Theanine - NOW Foods

The standard dosage that is the most common recommendation is 200mg per day.

Although going higher appears to be safe, I do not see much reason to go higher at this stage. We see clear benefits from L-Theanine at this dosage. I would only go higher if we start seeing evidence that higher dosages have even more benefits.

It takes L-Theanine 30-50 minutes to peak in the blood. Its half-life ranges from 58 to 74 minutes.

Based on that, it likely makes sense to take L-Theanine ~30 minutes before you want the benefits.

This could be 30 minutes before something stressful, or 30 minutes before bed, for example.


Although there is not really a wealth of research on L-Theanine, the research we have on it looks promising. There is not much downside to taking it either. If you experience a lot of stress in your life, it is likely worth trialling.

By Aidan Muir

Aidan is a Brisbane based dietitian who prides himself on staying up-to-date with evidence-based approaches to dietetic intervention. He has long been interested in all things nutrition, particularly the effects of different dietary approaches on body composition and sports performance. Due to this passion, he has built up an extensive knowledge base and experience in multiple areas of nutrition and is able to help clients with a variety of conditions. One of Aidan’s main strengths is his ability to adapt plans based on the client's desires. By having such a thorough understanding of optimal nutrition for different situations he is able to develop detailed meal plans and guidance for clients that can contribute to improving the clients overall quality of life and performance. He offers services both in-person and online.