L-theanine

L-theanine, an amino acid from tea, may slightly improve how well you feel you sleep. The effect is small, mostly self-reported, and many studies mixed it with other ingredients.

• Evidence: Weak
• Low effort
• Low cost
• Works: 2–8 weeks in trials

Why it matters

L-theanine is an amino acid found in tea leaves. It’s sold as a “calm” supplement that doesn’t make you drowsy. If it took the edge off evening stress, it might help you fall asleep. That’s the idea; the studies so far show only small effects, mostly on questionnaires.

How to do it

1. Dose used in trials: 200 mg a day in a trial of healthy adults [2], 400 mg a day in boys with ADHD [4], and 450–900 mg a day in adults with anxiety [3]. The 2025 meta-analysis said the right dose and duration still aren’t known [1].
2. Timing: in the healthy-adult trial, people took it before sleep each night [2]. In the ADHD trial, doses were taken at breakfast and after school [4]. There’s no clear evidence that one time of day is better.
3. Give it 4 weeks before you judge. The healthy-adult trial ran for four weeks [2].
4. Choose a single-ingredient product if you want to know what you’re testing. Many sleep products mix L-theanine with other ingredients, and the meta-analysis noted the lack of studies on L-theanine alone [1].
5. Don’t count on tea to deliver it. Tea also contains caffeine; see caffeine cutoff.

Check with a doctor or pharmacist first if you’re pregnant or breastfeeding, or take any regular medication. Memorial Sloan Kettering lists pregnancy and breastfeeding as reasons not to use it [5]. In the US, the FDA doesn’t approve dietary supplements before they’re sold; the maker is responsible for safety and labeling [6].

Side effects

Memorial Sloan Kettering reports no side effects from L-theanine itself [5]. In the ADHD trial, 400 mg a day for six weeks was well tolerated, with no significant adverse events [4]. These were short trials; long-term safety hasn’t been studied well.

Interactions

• Sedatives and sleeping pills (such as lorazepam, diazepam and zolpidem): taking them with L-theanine may increase drowsiness, so avoid the combination unless your doctor agrees [5].
• Antidepressants: in a trial of 46 adults with anxiety, L-theanine was added to their usual antidepressant for 8 weeks [3]. That one trial isn’t enough to call the combination safe for everyone, so ask your prescriber.
• Blood pressure medication and others: we found no official source listing interactions. That’s a gap in evidence, not proof of safety. Ask your pharmacist.

Common mistakes

• Expecting it to knock you out. It’s not a sedative, and the measured effects are small [1].
• Judging it on a blend. If your product also has melatonin, magnesium or herbs, you can’t tell which part helped [1].
• Assuming “natural” means no interactions. It may add to the effect of sedatives [5].

Effect on your sleep score

• Time to fall asleep: a small improvement in self-rated time to fall asleep across 10 studies (a standardized effect size of 0.15, which is small) [1]. In the healthy-adult trial, the questionnaire scores for time to fall asleep and sleep disturbance improved [2].
• Efficiency: in boys with ADHD, wrist trackers showed better sleep efficiency, but no change in time to fall asleep [4]. That’s children with a specific condition, so it may not apply to you.
• Deep sleep, REM, HRV, resting heart rate: we found no study measuring these in healthy adults with wearables.

How confident: low.

Evidence

Rated Weak. The 2025 meta-analysis included 19 trials with 897 people. L-theanine improved self-rated time to fall asleep, daytime functioning and overall sleep quality, all by small to moderate amounts. The authors flagged that few studies tested L-theanine on its own [1].

The healthy-adult trial was small: 30 people took 200 mg or placebo for four weeks each, in random order. Sleep questionnaire scores improved [2]. The L-theanine was made by Taiyo Kagaku, a company that sells it, and two of the authors worked there [2].

The best-designed adult trial was mostly negative. In 46 people with anxiety, L-theanine didn’t beat placebo for insomnia severity, though people were more satisfied with their sleep [3].

General information for healthy adults, not medical advice. If you have a sleep problem that lasts, read when to see a doctor. Sources checked 4 October 2026. Spot a mistake? Tell us.