L-theanine, caffeine jitters and the crash: what the research says

Last updated October 2026

You know the feeling. Your heart is going a little too fast, your hands are buzzing, and you are somehow more awake and less useful at the same time. A few hours later the floor drops out and you are reaching for the next cup.

L-theanine gets sold as the fix for both halves of that. It is an amino acid found in tea, and it now shows up in a lot of energy products, including ours. So we went through the research to see what it actually supports. Here is what we found, including the parts that do not flatter the category.

Why does caffeine make you jittery?

Jitters are a dose problem first. The FDA lists jitters, anxiety, a racing heart, palpitations and raised blood pressure among the symptoms of too much caffeine [1]. How much is "too much" depends on the person: the FDA notes "wide variation in both how sensitive people are to the effects of caffeine and how fast they eliminate it from the body" [1].

Some of that variation is genetic. One liver enzyme, CYP1A2, handles about 95% of the caffeine you take in, and common differences in that enzyme change how fast people clear it [2]. Habit matters too. In a double-blind study of 369 adults, regular caffeine users built up a tolerance to its jittery side, while for people who rarely had caffeine, the jitteriness was strong enough to cancel out the alertness benefit [3]. Mayo Clinic puts it simply: "If you don't drink daily, you might react more to it" [4].

As Nicole Clark, MD, told the American Medical Association: "if you're getting jittery, it's too much caffeine" [5].

Does L-theanine stop caffeine jitters?

Not reliably, based on the evidence so far. The best-known trial to measure jitteriness directly gave 48 adults 250 mg of caffeine, 200 mg of L-theanine, both, or neither. Caffeine raised alertness, jitteriness and blood pressure. Adding L-theanine blunted the blood pressure rise, but the authors found it "did not significantly affect jitteriness" [6].

Other studies point in different directions:

• Under stress, they cancelled out. In a 2017 study of 36 people given 200 mg of each, caffeine and L-theanine pushed attention in opposite directions, and "when consumed together, they counteract the effects of each other" [7].
• A 2026 trial did not measure jitters at all. It tested performance in 20 competitive athletes and found no added benefit from combining the two; the authors wrote that their results "challenge the prevailing assumption" that they work better together [8].

So the research does not show that L-theanine stops jitters. The one effect measured directly was on blood pressure, in one trial at 250 mg of caffeine and 200 mg of L-theanine, more of each than in an LSC100 lozenge. "Jitter-free" goes further than the research does.

What actually causes the caffeine crash?

There is no formal definition of a caffeine crash, but three well-documented things can leave you drained after your caffeine.

1. Withdrawal. If you have caffeine every day, missing your usual amount brings fatigue, low energy, poor focus and headaches. A review of 66 studies found symptoms usually start 12 to 24 hours after the last dose, peak between 20 and 51 hours, and can last 2 to 9 days. They showed up in people having as little as 100 mg a day [10].
2. Sleep debt. Caffeine can hide tiredness during the day and then cost you sleep at night, which makes the next day worse. Mayo Clinic describes exactly that loop [4]. In one sleep study, 400 mg of caffeine taken six hours before bed still disrupted sleep [11].
3. Sugar. The "sugar rush" does not hold up. A meta-analysis of 31 studies and 1,259 people found carbohydrates did not lift mood at any point, and were linked to more fatigue and less alertness in the first hour after eating them [12]. That matters if your caffeine comes in a large sweetened coffee drink or a full-sugar energy drink.

No study we found measured a "crash" in people taking caffeine with L-theanine, and none tested whether a sugar-free caffeine product avoids one. So we can't tell you L-theanine, or skipping sugar, prevents a crash. What you can control is the list above: keep your daily amount steady, protect your sleep, and watch the sugar that rides along with your caffeine.

Is there a best ratio of caffeine to L-theanine?

Nobody knows yet. Studies have used everything from 40 mg of caffeine with 97 mg of L-theanine to roughly 250 mg with 200 mg [6] [13]. We found no trial designed to find the best caffeine to L-theanine ratio, and the authors of the 2025 wrestling trial wrote that research "should also test varying CAF: THE dose ratios" [9].

For the record, LSC100 pairs 100 mg of caffeine with 100 mg of L-theanine. That is a 1:1 ratio, and it is a lower L-theanine dose than the side-effect studies above used. We would rather tell you that than point at a study that tested something else.

How much caffeine is in coffee, espresso and energy drinks?

It varies a lot by brand and brew, but these are common reference points from Mayo Clinic, citing USDA data [14]:

• Brewed coffee, 8 oz: about 96 mg
• Espresso, 1 oz: about 63 mg
• Energy drink, 8 oz: about 79 mg
• Black tea, 8 oz: about 48 mg

The FDA gives a wider range for energy drinks: 54 to 328 mg per 16 oz can [1]. A single LSC100 lozenge has 100 mg, so it lands near a cup of brewed coffee.

How much caffeine is too much?

For most healthy adults, the FDA cites 400 mg a day as an amount "not generally associated with negative effects," which it puts at about two to three 12 oz cups of coffee [1]. The European Food Safety Authority adds that single doses up to 200 mg do not raise safety concerns for healthy adults [15].

A few things to keep in mind:

• Count every source. Coffee, tea, soda, energy drinks, pre-workout and lozenges all add up toward the same daily total.
• Some people should be more careful. If you are pregnant, trying to get pregnant or breastfeeding, talk with your provider. ACOG advises staying under 200 mg a day in pregnancy [5]. Caffeine can make anxiety and seizure disorders worse, so if you have either, or take medication, ask a doctor or pharmacist first [4]. If you have a heart condition, the same goes [5].
• Not for kids or teens. The FDA notes that medical experts advise against energy drinks for children and teens [1].
• Stay away from pure caffeine powder. One teaspoon can hold as much caffeine as 28 cups of coffee, and these products have been linked to deaths in the US [16].

So where does that leave L-theanine?

The combination does have research behind it, just not for the reasons it usually gets marketed. A 2014 meta-analysis of 11 trials found moderate improvements in alertness and in accuracy when switching between tasks, in the first two hours after taking caffeine with L-theanine. It also found a trend suggesting the caffeine dose mattered more than the L-theanine dose [13]. A 2025 review of 50 trials was more cautious, saying the results left real uncertainty about the size, and sometimes the direction, of the effects [17].

Here is exactly what is in LSC100: 100 mg of caffeine from green coffee extract, 100 mg of L-theanine, and 0 g of added sugar, in Cold Brew Coffee and Crystal Fresh Mint. Whatever you take, a dose you can count is the most useful thing on the label. The rest is up to how much you take, when you take it, and how you sleep.

What to check, in order

1. Add up every source of caffeine in your day and keep it under 400 mg, or lower if your doctor says so.
2. If you get jittery, take less. A smaller dose fixes jitters more reliably than anything you add to it.
3. Keep your daily amount steady so you don't swing into withdrawal.
4. Stop caffeine at least eight hours before bed. One study found that even six hours was not enough [11].
5. Watch the sugar in your coffee drinks and energy drinks.
6. If you try L-theanine, treat it as a possible bonus, not a guarantee.

FAQ

Is natural caffeine gentler than synthetic caffeine?

No. The FDA says "there's no difference in the way your body handles" caffeine from coffee or tea and caffeine added to a product [1]. Ours comes from green coffee extract, and it works in your body the same way caffeine from any other source does.

Does L-theanine make you sleepy?

At the doses in these studies, it was not reported as a sedative. In the 2008 trial it slowed overall reaction time on one task [6].

How fast does a caffeine lozenge work?

We have not measured how fast LSC100 works, and we found no published study of caffeine lozenges. Until there is data, we won't make a speed claim.

This article is for general information only and is not medical advice. LSC100 is not intended to diagnose, treat, cure or prevent any disease. Talk to your doctor before using caffeine if you are pregnant or nursing, have a medical condition, or take medication. Not intended for anyone under 18.

Sources

1. U.S. Food and Drug Administration. "Spilling the Beans: How Much Caffeine is Too Much?" Content current as of August 28, 2024. https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much Symptoms of too much caffeine, individual variation, the 400 mg figure, energy drink ranges, natural vs added caffeine, advice for children and teens.
2. Nehlig A. "Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption." Pharmacological Reviews, 2018. Review. https://pubmed.ncbi.nlm.nih.gov/29514871/ CYP1A2 metabolizes 95% of ingested caffeine; genetic variation in clearance.
3. Rogers PJ, et al. "Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance." Psychopharmacology, 2013. Double-blind, n=369. https://pubmed.ncbi.nlm.nih.gov/23108937/ Tolerance to jitteriness in regular users; in non-regular users jitteriness offset the alertness benefit.
4. Mayo Clinic Staff. "Caffeine: How much is too much?" February 21, 2025. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20045678 Non-daily users react more; the sleep and caffeine loop; who should be careful.
5. Berg S. "What doctors want patients to know about the impact of caffeine." American Medical Association, July 6, 2026. https://www.ama-assn.org/public-health/prevention-wellness/what-doctors-want-patients-know-about-impact-caffeine Physician quotes on jitteriness and heart concerns; ACOG guidance of under 200 mg a day in pregnancy.
6. Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW. "Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together." Psychopharmacology, 2008. Randomized, double-blind, placebo-controlled, n=48; 250 mg caffeine, 200 mg theanine. https://pubmed.ncbi.nlm.nih.gov/17891480/ Theanine blunted the blood pressure rise but did not significantly affect jitteriness.
7. Giles GE, et al. "Caffeine and theanine exert opposite effects on attention under emotional arousal." Canadian Journal of Physiology and Pharmacology, 2017. Double-blind, n=36; 200 mg each. https://pubmed.ncbi.nlm.nih.gov/28044450/ Under stress, the two counteracted each other.
8. Yildirim Tuncer S, et al. Frontiers in Nutrition, 2026. Randomized, double-blind crossover, n=20 athletes; about 3 mg/kg caffeine, 200 mg theanine. https://pmc.ncbi.nlm.nih.gov/articles/PMC12884062/ Findings "challenge the prevailing assumption" that the two work better together. Side effects were not measured.
9. Razazan R, et al. Journal of the International Society of Sports Nutrition, 2025. Double-blind crossover, n=12 wrestlers, low habitual caffeine users; 3 mg/kg each. https://www.tandfonline.com/doi/full/10.1080/15502783.2025.2564238 Authors call for testing different caffeine to L-theanine ratios. The paper reports conflicting participant ages, so we do not cite its side-effect results.
10. Juliano LM, Griffiths RR. "A critical review of caffeine withdrawal." Psychopharmacology, 2004. Review of 57 experimental and 9 survey studies. https://pubmed.ncbi.nlm.nih.gov/15448977/ Withdrawal onset, peak and duration; symptoms at doses as low as 100 mg a day.
11. Drake C, et al. "Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed." Journal of Clinical Sleep Medicine, 2013. 400 mg dose. https://pmc.ncbi.nlm.nih.gov/articles/PMC3805807/ Caffeine six hours before bed still disrupted sleep.
12. Mantantzis K, et al. "Sugar rush or sugar crash? A meta-analysis of carbohydrate effects on mood." Neuroscience and Biobehavioral Reviews, 2019. 31 studies, 1,259 participants. https://pubmed.ncbi.nlm.nih.gov/30951762/ No mood lift from carbohydrates; more fatigue and less alertness in the first hour.
13. Camfield DA, et al. "Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood." Nutrition Reviews, 2014. Meta-analysis of 11 RCTs. https://pubmed.ncbi.nlm.nih.gov/24946991/ Moderate effects on alertness and task-switching accuracy in the first 2 hours; caffeine dose mattered more than theanine dose.
14. Mayo Clinic Staff. "Caffeine content for coffee, tea, soda and more." February 6, 2025 (USDA data). https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20049372 Caffeine amounts per drink.
15. EFSA Panel on Dietetic Products, Nutrition and Allergies. "Scientific Opinion on the safety of caffeine." EFSA Journal, May 27, 2015. https://www.efsa.europa.eu/en/efsajournal/pub/4102 Single doses up to 200 mg raise no safety concern for healthy adults.
16. U.S. Food and Drug Administration. "Pure and Highly Concentrated Caffeine." Modified March 6, 2023. https://www.fda.gov/food/information-select-dietary-supplement-ingredients-and-other-substances/pure-and-highly-concentrated-caffeine One teaspoon of powder equals about 28 cups of coffee; linked to deaths.
17. Payne et al. Nutrition Reviews, 2025. Systematic review of 50 RCTs. https://pmc.ncbi.nlm.nih.gov/articles/PMC12422004/ Small to moderate effects with wide uncertainty.