What Does L-Theanine Do? Benefits, Dosage and When to Take It
L-theanine is an amino acid found almost only in tea leaves. It isn't a stimulant or a sedative. In studies it promotes a relaxed but alert state: it reaches its peak in your blood within about an hour, and at 200 mg a day for four weeks it improved stress, sleep and focus ratings in healthy adults. Most studies used between 100 and 400 mg a day, and side effects are rare.
It's the reason a cup of tea feels different from a cup of coffee, even though both have caffeine. Here's what L-theanine is, what the research shows, how much to take, how fast it works and how long it lasts.
What is L-theanine?
L-theanine is an amino acid made by the tea plant, Camellia sinensis, the source of green, black, white and oolong tea. It's not one of the amino acids your body uses to build protein. It's chemically similar to glutamate, one of the brain's main signaling chemicals, and it reaches the brain after you swallow it.
You get some from every cup of tea. A 2008 study put the amount in a cup of black tea at about 20 mg. Supplements usually contain 100 to 200 mg per serving, which is why most of the research uses supplements rather than tea.
What does L-theanine do? What the research shows
The human studies are mostly small, but they point the same way: calmer without being drowsy.
- A relaxed, alert brain state. In a 2008 brain-wave study, just 50 mg of L-theanine increased alpha activity, a pattern linked to relaxed alertness, over the 45 to 105 minutes after people took it, compared with a placebo. The researchers described it as relaxing the mind without causing drowsiness.
- A calmer response to stress. In a 2007 study of 12 people doing a stressful mental arithmetic task, 200 mg of L-theanine reduced the rise in heart rate and in a stress marker in saliva compared with placebo.
- Better stress, sleep and focus scores over four weeks. In a 2019 placebo-controlled trial, 30 healthy adults took 200 mg a day for four weeks. Their scores for stress-related symptoms went down, their sleep quality scores improved, and they did better on tests of verbal fluency and executive function.
- The overall picture. A 2020 systematic review of nine randomized trials concluded that 200 to 400 mg a day may help reduce stress and anxiety in people under stressful conditions, and called for larger, longer studies.
One thing worth saying plainly: some authors of the 2007 and 2019 studies worked for a company that makes L-theanine. The results are consistent with independent work, but it's fair to know.
L-theanine also has two well-studied pairings. With caffeine, it improved focus and attention in several trials, which we cover in L-theanine and caffeine. At night, trials found it helped people fall asleep a little sooner and rate their sleep better, which is in L-theanine for sleep.
How long does L-theanine take to work, and how long does it last?
It's absorbed quickly. In a 2012 study, blood levels peaked about 50 minutes after a 100 mg dose, and the timing was the same whether people took it as a capsule or in green tea. Most single-dose studies measured their effects within the first one to two hours, and the brain-wave study above saw changes from 45 minutes on.
How long it lasts is less precisely known. The single-dose effects in studies were measured over a couple of hours, and blood levels fall back over the following hours as the body breaks it down. The longer-term changes in stress and sleep ratings came from daily use over four weeks, so if that's your goal, judge it over weeks, not days.
L-theanine dosage: how much to take
There's no official recommended amount, because L-theanine isn't an essential nutrient. The studies give a good guide:
| Amount | What it was used for |
|---|---|
| About 20 mg | A cup of black tea |
| 50 mg | Increased relaxed-alert brain waves within two hours |
| 97 to 250 mg | Paired with caffeine for focus and attention |
| 200 mg a day | Four-week trial: stress, sleep and focus ratings |
| 200 to 400 mg a day | The range a 2020 review linked to lower stress |
Put on one scale, the gap between a cup of tea and the amounts the studies used is easier to see:
In practice, most people take 100 to 200 mg once a day, and some take a second dose later in the day. If you're new to it, start at the lower end and see how you feel. Follow the label of whatever product you use, and don't stack several L-theanine products on top of each other without adding them up.
When is the best time to take L-theanine?
It depends on what you want from it:
- For focus during the day: in the morning, often with your coffee or tea. The pairing with caffeine is the best-studied use.
- For a stressful stretch: about 30 to 60 minutes before it, since blood levels peak in under an hour.
- For winding down: in the evening, 30 to 60 minutes before bed.
- For the four-week effects: at the same time every day, whichever time you'll remember.
Does L-theanine make you sleepy?
Not usually. It's not a sedative, and in the brain-wave study it relaxed people without making them drowsy, which is why it's popular during the workday. Some people do feel more relaxed after taking it in the evening, and that calm can make it easier to fall asleep, but it won't knock you out the way a sleeping pill does.
L-theanine side effects and safety
For most healthy adults, L-theanine is very well tolerated. Memorial Sloan Kettering's herb database says side effects haven't been reported for L-theanine itself, and in trials they've been rare and mild.
Check with your doctor first if you:
- Are pregnant or breastfeeding, since there's little research on it in pregnancy
- Take blood pressure medication, sedatives or stimulant medication
- Are giving it to a child
Taking L-theanine with other supplements
- Magnesium: a common evening pairing, and there's no known interaction between them. Both are used for winding down, in different ways, and we cover the magnesium side in magnesium for sleep.
- Ashwagandha: often taken together for everyday stress. We explain how they differ and how to take them in ashwagandha and L-theanine.
- Caffeine: the best-studied pairing of all, covered in L-theanine and caffeine.
L-theanine in our gummies
Our Shilajit Gummy carries 120 mg of L-theanine, inside the 100 to 200 mg range most people take, along with 25 mg of shilajit, 37 mg of magnesium malate, 30 mg of zinc and vitamins B6 and D3. The label says one a day with a meal, which makes breakfast the natural time, and it has no caffeine, so it sits alongside your coffee or tea rather than adding to it. Every amount is printed on the jar beside its ingredient. Our other daytime gummies are in Calm & Focus.
Frequently asked questions
What does L-theanine do?
It promotes a relaxed but alert state. In studies it increased relaxed-alert brain waves, softened the body's response to a stressful task, and over four weeks of daily use improved stress, sleep and focus ratings.
How much L-theanine should I take?
Most people take 100 to 200 mg a day. Studies used from 50 mg up to 400 mg a day. Start low and follow your product's label.
How long does L-theanine take to work?
Blood levels peak about 50 minutes after you take it, and most studies measured effects within the first one to two hours. Effects on stress and sleep ratings were measured after four weeks of daily use.
Is it safe to take L-theanine every day?
For most healthy adults, yes. Trials have used it daily for weeks, and side effects have been rare and mild. Check with your doctor if you're pregnant, breastfeeding or take regular medication.
Does L-theanine lower cortisol?
The evidence is limited. The best-known stress studies measured heart rate, a saliva stress marker and questionnaire scores rather than cortisol, and those improved. It's fair to say it may soften the body's stress response, not that it reliably lowers cortisol.
Can I take L-theanine with coffee?
Yes, and it's the best-studied combination. Together they improved focus and attention in several trials. Keep your total caffeine sensible.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is general information and not medical advice. Talk to your healthcare provider before starting any supplement, particularly if you are pregnant or nursing, take prescription medication, or are sensitive to caffeine.