Does L-Theanine Lower Your Heart Rate? The Trial Record
Does L-Theanine Lower Your Heart Rate? The Trial Record
Not at rest, as far as trials show. In one small placebo-controlled study (n=12), L-theanine reduced the heart-rate jump during a stressful math task compared to placebo. Other placebo-controlled trials at 200 mg found no heart-rate change or did not report one. The evidence points to a possible blunting of stress-driven heart-rate spikes, not a lower resting pulse.
Every Human Trial That Measured Heart Rate
Five placebo-controlled human trials are the closest evidence; three report a heart-rate result and two report only blood pressure in their abstracts. The table below lists each one, what it found, and any industry ties.
| Trial | n | Theanine dose | Setting | Heart-rate result | Note |
|---|---|---|---|---|---|
| Kimura et al., Biol Psychol 2007 | 12 | Not stated in abstract | Mental arithmetic stress, placebo-controlled, double-blind | Reduced heart-rate response to stress vs placebo | HRV suggested lower sympathetic activation |
| Williams et al., Foods 2020 | 18 enrolled, 11 completed | 200 mg in mango sorbet | 90 min monitoring, placebo sorbet | No difference in heart rate, BP, or HRV | Pilot; food matrix; authors declared no conflict |
| Evans et al. (AlphaWave), Neurol Ther 2021 | Moderately stressed healthy adults | 200 mg | Mental arithmetic stress, triple-blind crossover | Heart rate rose during stress in both arms; no heart-rate benefit reported | Funded by Ethical Naturals (AlphaWave maker) |
| Rogers et al., Psychopharmacology 2008 | 48 | 200 mg (with or without 250 mg caffeine) | Rest, 40 min after dose | Heart rate not reported in abstract; theanine offset caffeine's BP rise | |
| Yoto et al., J Physiol Anthropol 2012 | 14 | 200 mg | Mental and physical stress tasks | Heart rate not reported in abstract; BP rise attenuated in high-responders | Theanine supplied by Taiyo Kagaku |
Source: trial abstracts on PubMed, checked Oct 2026. Industry ties noted where the paper states them.
Why Theanine Might Affect Heart Rate Under Stress
The Kimura 2007 trial is the only one showing a clear heart-rate effect, and the direction matters: theanine did not slow a resting heart, it blunted how much the heart rate climbed during arithmetic stress. The authors' HRV analysis pointed to reduced sympathetic nervous system activation, the fight-or-flight branch that speeds the heart when you are under pressure.
Kimura et al. point to theanine's ability to block glutamate binding as one possible route. Later trials looked at a different stress marker, cortisol: the AlphaWave trial (industry-funded by Ethical Naturals) found a greater salivary cortisol decrease at one hour with 200 mg theanine vs placebo, and White et al. 2016 reported a reduced cortisol response at three hours in a separate crossover trial of 34 adults given a theanine-based nutrient drink with other ingredients, not pure theanine.
But cortisol is not heart rate. A cortisol result does not tell you what happened to heart rate.
Does L-Theanine Lower Resting Heart Rate?
No trial in this review shows a lower resting heart rate in healthy adults. The Williams et al. 2020 pilot monitored heart rate, blood pressure, and HRV for 90 minutes after a 200 mg dose in mango sorbet and found no reduction in any of those measures. That trial was small (11 completers) and delivered theanine in a food matrix, but it is the most direct resting data in this review.
The AlphaWave crossover trial also saw heart rate rise during stress in both the theanine and placebo arms; in the full text, the theanine arm actually showed larger heart-rate increases at 3 and 6 minutes after dosing.
L-Theanine with Caffeine: Heart Rate and Blood Pressure
If you pair L-theanine with caffeine, the blood pressure data is clearer than the heart-rate data. Rogers et al. 2008 (n=48) gave participants 250 mg caffeine, 200 mg theanine, both, or neither. Caffeine raised blood pressure and self-rated jitteriness. Theanine antagonized the blood-pressure rise but did not significantly change jitteriness, and the abstract does not report a heart-rate result.
Yoto et al. 2012 compared 200 mg theanine and 100 mg caffeine in separate sessions: theanine significantly blunted blood-pressure increases during mental and physical tasks in participants whose BP responded the most, and caffeine tended to have a similar but smaller effect. Again, heart rate was not reported in the abstract. Theanine in that trial was supplied by Taiyo Kagaku.
For a fuller look at that pairing, see the caffeine and L-theanine research and the trial-level ratio data. The L-theanine and blood pressure page covers the BP side in detail.
Can L-Theanine Cause Heart Palpitations?
No trial in this review reports palpitations as a side effect of L-theanine. The AlphaWave trial described 200 mg as "safe and well tolerated" in its moderately stressed cohort.
If a product combining caffeine and theanine makes your heart race, caffeine is the more likely culprit. A 2017 review in Frontiers in Psychiatry noted that caffeine at typical doses produces "mild changes in heart rate and blood pressure." New, persistent, or uncomfortable palpitations warrant a visit to your doctor, not a supplement adjustment. More on tolerability at the L-theanine side effects review.
Talk to a Clinician First If
- You take blood pressure or heart-rhythm medication. No trial in this review tested L-theanine alongside these drugs.
- You have a diagnosed heart condition or new, unexplained palpitations. Supplements are not a substitute for medical evaluation.
- You are pregnant or breastfeeding.
- You take sedatives or psychiatric medications (see L-theanine interactions).
L-theanine is not a treatment for any heart condition.
Where the 60 mg in Roon Fits
Roon contains 60 mg L-theanine alongside 80 mg caffeine per pouch. The trials above that state a dose used 200 mg, roughly 3.3 times that amount, so their results should not be projected onto a 60 mg dose. Theanine's role in the Roon formula is to smooth caffeine's subjective edge, not to change heart rate or blood pressure.
Related from Roon
- L-Theanine and Blood Pressure: What Trials Show
- Caffeine and L-Theanine: The Research
- L-Theanine: The Complete Guide
Frequently Asked Questions
How long does L-theanine take to work?
In White et al. 2016, subjective stress reduction appeared about one hour after a theanine-based nutrient drink (which contained other ingredients alongside L-theanine), while the cortisol response shifted at three hours. For timing details, see how long L-theanine takes to work.
Is 200 mg of L-theanine safe?
A systematic review of RCTs (Williams et al. 2020) found that 200 to 400 mg per day may help reduce stress and anxiety in people under stressful conditions, and called for larger, longer trials. Hidese et al. 2019 gave 200 mg daily for four weeks in a crossover design, though two co-authors were employed by the theanine supplier (Taiyo Kagaku). Long-term safety data beyond a few weeks remains limited.
Does L-theanine lower cortisol?
Two trials found cortisol effects. White et al. 2016 reported a reduced cortisol response at three hours in 34 healthy adults given a theanine-based nutrient drink (L-theanine with other ingredients), not pure theanine. The AlphaWave trial found a greater cortisol decrease at one hour vs placebo, but that study was funded by Ethical Naturals, the ingredient's maker. Neither trial measured long-term cortisol levels.
Can I take L-theanine with a beta blocker?
No trial in this review tested L-theanine alongside beta blockers or other heart-rate medications. Ask your prescriber before combining them. See L-theanine interactions for a broader list.
Caffeine and Theanine, Built for a Calm Afternoon
The trial record above suggests theanine may take the edge off a stress response, not slow a resting heart. Roon pairs 60 mg L-theanine with 80 mg caffeine in a zero-nicotine pouch, aiming for no jitters and no crash; at 60 mg it sits well below the trial doses, so none of the heart-rate or blood-pressure results above apply to it directly.
The other half of the formula targets duration. Methylliberine (Dynamine, 25 mg) slowed caffeine clearance in a randomized, double-blind crossover PK study (n=12): caffeine's half-life extended from 7.2 to 15 hours and oral clearance dropped from 41.9 to 17.1 L/hr, with no increase in peak concentration (study). That study dosed 100 mg methylliberine plus 150 mg caffeine, about 4x the methylliberine and 1.9x the caffeine in a Roon pouch, so the mechanism is directionally the same but the magnitude will differ. A slower clearance number is not the same as hours of felt focus; one pouch is typically felt for 6 to 8 hours. Allow at least eight hours between your last pouch and sleep.
Roon costs from $9.16 per tin on a subscription, as little as $0.61 per pouch. If you have a heart condition or take heart-rate medication, check with your doctor before adding any caffeine product.
Sources
- Kimura K et al., Biol Psychol 2007;74(1):39-45. PubMed
- Williams J et al., Foods 2020;9(3):371. PubMed
- Evans M et al., Neurol Ther 2021;10:1061-1078. PubMed (Funded by Ethical Naturals)
- Rogers PJ et al., Psychopharmacology 2008;195(4):569-77. PubMed
- Yoto A et al., J Physiol Anthropol 2012;31:28. PubMed (Theanine supplied by Taiyo Kagaku)
- White DJ et al., Nutrients 2016;8(1):53. PubMed
- Hidese S et al., Nutrients 2019;11(10):2362. PubMed (Co-authors employed by Taiyo Kagaku)
- Williams JL et al., Plant Foods Hum Nutr 2020;75:12-23. PubMed
- Temple JL et al., Front Psychiatry 2017;8:80. PMC
Written by Roon Team
