What's in tea that keeps you awake?

January 6, 2026 •

4 min read

According to the Sleep Foundation, while L-theanine in tea promotes relaxation, caffeine acts as a central nervous system stimulant, creating the complex effect of what's in tea that keeps you awake. Tea is the second-most widely consumed beverage globally, but its ability to promote alertness is a common source of inquiry.

Quick Summary

Several compounds, primarily caffeine, along with the methylxanthines theophylline and theobromine, contribute to tea's stimulating effects. These ingredients work in synergy with the amino acid L-theanine, which promotes relaxation, to influence alertness and focus.

Key Points

Caffeine is the primary stimulant: As a central nervous system stimulant, caffeine blocks adenosine receptors in the brain, reducing feelings of tiredness and promoting wakefulness.
L-Theanine creates calm focus: The amino acid L-theanine promotes relaxation and increases alpha brain waves, which helps counteract the jittery effects of caffeine and leads to a state of calm alertness.
Theophylline and Theobromine contribute: These other methylxanthines also contribute to tea's stimulating effects, with theophylline affecting the respiratory system and theobromine providing a milder, more sustained energy boost.
Brewing method matters: The amount of caffeine and other compounds extracted depends on the steeping time and water temperature, with longer and hotter brews yielding more potent results.
Individual sensitivity varies: Genetic factors and metabolism rates determine how intensely an individual responds to the caffeine in tea, with some people being more sensitive than others.
Decaf tea isn't caffeine-free: Decaffeinated tea has only trace amounts of caffeine, while herbal teas contain no caffeine and offer a safe, calming alternative for evening consumption.

The reason certain teas prevent sleep and boost alertness is a combination of specific compounds that interact with the body's central nervous system. While many people associate caffeine almost exclusively with coffee, it is also a naturally occurring component of tea leaves from the Camellia sinensis plant. The stimulating effect isn't a simple dose-response, however, as other components in tea leaves can either enhance or mitigate caffeine's effects, creating a unique experience compared to other caffeinated beverages.

The Primary Culprits: Caffeine, Theophylline, and Theobromine

How Caffeine Creates Alertness

Caffeine is the most recognized stimulant in tea, coffee, and other common beverages. It works by blocking adenosine, a neurotransmitter that promotes sleep and relaxation. As caffeine prevents adenosine from binding to its receptors in the brain, it reduces feelings of fatigue and increases alertness. This is the primary reason why a cup of tea can leave you feeling energized and focused. The amount of caffeine can vary significantly depending on the tea type, with black and matcha teas generally containing higher levels than green or white teas.

The Role of Theophylline

Tea also contains other methylxanthines, a class of alkaloids that includes caffeine. Theophylline is one of these compounds and is also known for its stimulating properties. Unlike caffeine, theophylline has a more pronounced effect on the respiratory system, acting as a bronchodilator. It can also contribute to wakefulness, and studies have shown it can disturb sleep, particularly in individuals who are sensitive to caffeine. This means that for some, theophylline adds to the difficulty of falling asleep after consuming certain teas.

The More Relaxed Stimulant: Theobromine

Theobromine is another methylxanthine found in tea, though it is more famously associated with cacao. While a stimulant, its effects are often described as milder and longer-lasting than caffeine, without the same sharp energy spike and subsequent crash. Theobromine primarily acts on the body's circulation, dilating blood vessels and boosting heart function, and has a less intense effect on the central nervous system compared to caffeine.

The Balancing Act: L-Theanine

Tea's stimulant effects are not just about its energizing components. A remarkable balancing act is performed by the amino acid L-theanine, which is also naturally present in tea leaves. L-theanine is known to promote relaxation without causing drowsiness by increasing alpha brain wave activity. This creates a state of 'calm alertness,' counteracting the jittery and anxious feelings that high doses of caffeine can cause. This unique combination of L-theanine and caffeine is a key differentiator between the stimulating effects of tea and coffee.

Factors Affecting a Tea's Kick

Beyond the intrinsic chemical composition, several factors influence how much of these compounds end up in your cup:

Type of Tea: While most 'true' teas (black, green, white) from the Camellia sinensis plant contain these compounds, the concentrations vary significantly. Black tea is generally highest in caffeine, followed by oolong, green, and white tea.
Brewing Time and Temperature: Steeping tea for longer periods or at higher temperatures extracts more caffeine and other compounds into the water. A short, quick steep will yield a less stimulating brew, while a longer steep will create a stronger effect.
Decaffeination Process: Decaf teas are not completely caffeine-free. The decaffeination process typically removes 90-97% of the caffeine, but trace amounts remain. Naturally caffeine-free herbal teas, such as chamomile or peppermint, contain no caffeine.
Genetics and Sensitivity: Individual sensitivity plays a major role in how tea affects a person. Those with a genetic predisposition for slower caffeine metabolism will feel the effects more intensely and for a longer duration.

Comparison of Key Tea Components


Component	Type	Primary Effect	Interaction in Tea
Caffeine	Methylxanthine	Blocks adenosine receptors, increasing alertness and wakefulness.	Counterbalanced by L-theanine, providing a smoother, more sustained energy boost.
L-Theanine	Amino Acid	Increases alpha brain waves, promoting relaxed focus without sedation.	Mitigates caffeine's jittery side effects, leading to a state of calm alertness.
Theophylline	Methylxanthine	Bronchodilator, stimulates central nervous system, can disturb sleep.	Contributes to the stimulating effects, especially in caffeine-sensitive individuals.
Theobromine	Methylxanthine	Milder stimulant with longer-lasting, less intense energizing effects.	Modulates the overall stimulating effect alongside caffeine and theophylline.

Conclusion: A Complex, Personal Beverage

In summary, the stimulating effect of tea is a multifaceted result of its chemical makeup. The primary driver is caffeine, a central nervous system stimulant, complemented by smaller amounts of other methylxanthines like theophylline and theobromine. However, the presence of L-theanine, a relaxing amino acid, mellows the typical caffeine buzz, leading to a state of focused calm rather than jitteriness. The exact impact of any given cup of tea depends on the tea type, preparation method, and individual genetic sensitivity to its components. For those seeking energy, choosing a high-caffeine black tea with a long steep time will maximize the stimulant effect. For a more balanced, relaxed focus, green tea provides the ideal blend of caffeine and L-theanine. Ultimately, understanding these components empowers individuals to choose the right tea for their desired effect, whether for sustained energy or a calm moment of reflection.

Visit the official website of the National Center for Biotechnology Information (NCBI) for in-depth studies on the effects of caffeine and other methylxanthines on the human body.

Frequently Asked Questions

The primary substance in tea that keeps you awake is caffeine, a natural stimulant that blocks the effects of adenosine, a neurotransmitter that signals the brain to feel tired.

Caffeine is present in 'true' teas like black, green, and white tea, which come from the Camellia sinensis plant. Herbal teas, or tisanes, are naturally caffeine-free as they are not made from these leaves.

Tea contains the amino acid L-theanine, which promotes relaxation and increases alpha brain wave activity. This effect works alongside caffeine to provide a state of focused calm, offsetting the anxiety and jitters often associated with coffee.

To reduce the caffeine in your tea, you can use cooler water, steep for a shorter amount of time, or use whole-leaf tea instead of tea bags, as whole leaves release caffeine less quickly.

Yes, tea also contains other methylxanthine stimulants like theophylline and theobromine, which contribute to its energizing effects, although to a lesser degree than caffeine.

Decaf tea contains only trace amounts of caffeine, making it a much safer option for consumption before bed than regular tea. For a completely caffeine-free option, naturally herbal teas are recommended.

L-theanine doesn't make you sleepy but can improve sleep quality by promoting relaxation and calming brain activity. This effect helps balance the stimulating aspects of caffeine.