Do L-theanine and caffeine mix? (2024)

L-theanine (N-ethyl-L-glutamine) is an amino acid found in green, oolong, matcha, white, and black tea leaves. It has the highest concentrations in green tea. If a daily cuppa isn’t your thing, you can still reap the potential health benefits of L-theanine, such as improved alertness and better sleep. It is also available in supplement form, often in combination with caffeine. Both substances are considered nootropics—“cognitive enhancers” or “brain boosters.” When combined, caffeine and L-theanine are said to improve focus and enhance cognitive function. Keep reading to learn the best ways to mix these two substances to reap the wellness benefits.

Does L-theanine have caffeine in it?

You’re likely consuming L-theanine and caffeine if you’re drinking caffeinated tea.

While L-theanine itself doesn’t contain caffeine, the two psychoactive compounds sometimes occur naturally together and are marketed as a combination in supplement form. For example, your average cup of green tea has about 20 mg to 40 mg of theanine and 30 to 50 mg of caffeine, according to Jaclyn Sklaver, MS, an integrative sports nutritionist in Miami, Florida. Dietary supplements often contain 100 mg to 200 mg of L-theanine, she says.

While the combination of L-theanine and caffeine is popular in supplements because of its benefits on cognition and mood, L-theanine is also available as a standalone supplement without caffeine that you can take alone or with your morning coffee.

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Does caffeine affect L-theanine?

Caffeine may improve the way L-theanine works and vice versa. Combining these two ingredients has some benefits.

Reduced side effects of caffeine

As a stimulant, caffeine can increase alertness, improve focus and cognitive function, and enhance physical performance and energy levels. However, it also causes increased blood pressure, respiration rates, and heart rates. According to research, L-theanine helps mitigate some of these adverse effects. L-theanine is known for its calming properties that help to counteract some of the less pleasant side effects of caffeine, like jitteriness and anxiety, says Jeanette Giacinto, a registered dietitian based in Long Beach, NY.

L-theanine, particularly when combined with magnesium, has also been shown to directly influence GABA (gamma-aminobutyric acid) receptors in the brain. GABA is an inhibitory neurotransmitter that has a calming effect on the central nervous system. It also increases brain levels of serotonin and dopamine, known as the “feel-good” hormones. It is believed that L-theanine increases levels of GABA in the brain, causing this calming and relaxing effect.

Increased alertness

One small placebo-controlled study found that combining caffeine and L-theanine improved cognitive performance, attention, and alertness more than caffeine alone. An older clinical trial compared the effects of 50 mg of caffeine with or without 100 mg of L-theanine in healthy volunteers while performing cognitively demanding tasks. The L-theanine/caffeine group experienced increased speed and accuracy of performance on attention-switching tasks and reduced distraction.

Improved cognition

These cognitive-enhancing effects show promise for individuals with attention deficit hyperactivity disorder (ADHD), too. According to a 2021 systematic review and meta-analysis, the combination of L-theanine and caffeine has positive effects on short-term sustained attention and overall cognition.

Caffeine and L-theanine have a complementary effect on chemicals in your brain called neurotransmitters, says Sklaver. Combining the two compounds can enhance cognition, increase alertness and focus, and reduce adverse caffeine side effects.

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Side effects of L-theanine and caffeine

“There are minimal risks or negative side effects associated with combining low-to-moderate doses of L-theanine and caffeine,” says Giacinto. Studies suggest that L-theanine and caffeine can cause headaches, but no other side effects have been reported. That said, the effects of caffeine are well-documented. According to the U.S. Food and Drug Administration (FDA), excess caffeine intake can cause:

• Jitters
• Nervousness
• Anxiety
• Insomnia
• Fast heart rate
• Nausea
• Upset stomach (dyspepsia)
• Unhappiness (dysphoria)
• Headache

While no significant adverse side effects are associated with L-theanine, it’s always recommended to consult a healthcare professional before starting any new supplement regimen, especially if you have any pre-existing medical conditions or are taking prescription or over-the-counter medications.

How to take L-theanine with coffee

If coffee is your preferred caffeinated beverage, Giacinto recommends taking L-theanine with caffeine about 30 minutes before you need to complete a task or start your workday. “Keep in mind that although L-theanine reduces the disruption that caffeine has on sleep, it’s still important to limit caffeine late in the day in order to not disrupt sleep patterns,” she says.

The best dose of L-theanine and coffee can vary by individual tolerance, but a 1:2 ratio of caffeine to L-theanine is recommended, says Sklaver. The average cup of coffee contains just under 100 mg of caffeine, so you’d add a 200 mg dose of L-theanine. Sklaver recommends taking the L-theanine at the same time as your coffee since they work synergistically together.

Giacinto says that because L-theanine is an amino acid, it may be best absorbed on an empty stomach, especially without protein-containing foods. But if you experience stomach upset or nausea, it’s okay to take it with food, such as a small meal or snack.

L-theanine is believed to be safe for daily use in healthy adults but always check with your healthcare provider or pharmacist before starting a new supplement. If you’re pregnant or breastfeeding, you should avoid L-theanine supplementation. It should also not be taken with antihypertensives, medications that lower blood pressure.

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The bottom line

L-theanine and caffeine are a dynamic duo for cognitive enhancement. Research shows that pairing the nootropics improves reaction times during complex tasks, increases subjective alertness, and decreases distractibility. If you’re looking for a way to improve your focus and attention, L-theanine and coffee may be just the ticket.