Theanine: Benefits & Side Effects

Medically Reviewed by Shruthi N, MD on October 23, 2024
5 min read

Theanine, also known as L-theanine, is an amino acid. It is found in tea leaves, especially in green tea and loose-leaf teas. You can consume L-theanine by drinking matcha, green tea, or white tea. It can also be taken as a dietary supplement in tablet or pill form. L-theanine may offer several health benefits, such as lowering anxiety and improving sleep quality.

L-theanine may enhance both relaxation and alertness. The effects largely depend on when and what it’s paired with. Responses to L-theanine may differ from person to person, and while it shows potential benefits for improving cognitive and mental concerns, more research is needed.

Mental focus 

Some research shows that L-theanine may help boost and sharpen your mental focus if you are experiencing brain fog.

For the greatest benefit, consider taking L-theanine during the day along with coffee or other caffeinated drinks.

Improved sleep conditions

Combining L-theanine with certain supplements may help improve the quality of your sleep. Supplements with gamma aminobutyric acid (GABA), a natural chemical messenger in your brain that's known for its calming effects, may improve the amount of hours of sleep you get and help with rapid eye movement (REM) sleep.

If you have sleep concerns, you can try taking L-theanine in the evening and avoid combining it with caffeine before bedtime. It's generally considered safe to take L-theanine with melatonin. 

L-theanine may not be as effective for treating more serious sleep conditions such as sleep apnea or insomnia. Ask your health care provider before you consider combining L-theanine with other prescription medications.

Less anxiety and stress

 L-theanine supplements may help boost your levels of GABA, serotonin, and dopamine, which can lead to better relaxation and less anxiety.

A recent study found a reduced stress-related symptoms in people who took L-theanine for four weeks. 

Keep in mind that each person handles stress in their own way, and the effects of L-theanine may vary from person to person. 

Theanine for attention deficit hyperactivity disorder (ADHD)

A recent study that looked at focus, mental processing, and impulse control in male children with ADHD found that the combination of L-theanine and caffeine may work as a promising option for managing ADHD symptoms.

The results revealed that L-theanine and caffeine seemed to boost attention span, reduce impulses, and improve cognitive abilities.

It also showed that L-theanine and caffeine helped lower brain activity in the default mode network (DMN), which possibly can improve mind wandering in people with ADHD.

Standard doses of theanine have not been set for any condition. Ingredients in supplements may vary widely. This makes it very hard to set a standard dose.

You can naturally get L-theanine by drinking teas such as matcha, green tea, and white tea. It has a unique caramel taste that helps reduce the bitterness of caffeine. You can also take L-theanine as a dietary supplement.

Theanine is also found in some mushrooms.

 L-theanine has been regarded as generally safe for most people. However, before starting any new supplement, it’s important to speak with your health care provider, especially if you have existing health problems or are currently taking any medications.

Theanine side effects 

The recommended daily intake of L-theanine is no more than 500 milligrams (mg). For most healthy adults, a daily dose between 200 mg and 500 mg is considered safe and effective. 

Side effects of L-theanine have not been reported. If you are drinking large amounts of tea to consume L-theanine, it may cause effects similar to those from a high intake ofcaffeine , such asupset stomach and irritability.

These side effects can include: 

  • Headaches
  • Stomach pain
  • Nausea
  • Dizziness
  • Fidgety or restless
  • Moodiness
  • Diarrhea

Risk factors 

The side effects of L-theanine are usually mild and uncommon. People who are pregnant or breastfeeding should be cautious when taking L-theanine, due to the limited research available for these groups. 

If you are using sleep medications such as lorazepam (Ativan®), diazepam (Valium®), or zolpidem (Ambien®), talk with your health care provider before taking L-theanine. It may lead to increased drowsiness. 

Similar to all supplements, it’s important to note that L-theanine products are not reviewed or regulated by the U.S. FDA. If you are thinking about trying L-theanine in supplement form, consider choosing a high quality product that doesn’t have any added fillers.

Theanine interactions 

Before taking L-theanine supplements, talk with your health care provider, if you regularly take any medications. Some sleep medications such as diazepam (Valium), lorazepam (Ativan), and zolpidem (Ambien) may interact with L-theanine and cause more drowsiness. It may also interact with sedatives, stimulants, and medications for high blood pressure.

Supplements are not regulated by the FDA in the same way that drugs are. The FDA does not review these supplements for safety or efficacy before they hit the market.

Tell your doctor about any supplements you're taking, even if they're natural. That way, your doctor can check on any potential side effects or interactions with medications.

L-theanine is an amino acid known for its calming effects. It's primarily found in green tea, matcha, and white tea. L-theanine may offer a wide variety of positive health benefits such as improved mental focus and sleep quality. When taken with caffeine, L-theanine might boost alertness and concentration. It may also help to reduce anxiety.

You can naturally get L-theanine from drinking tea. You can also take it as a dietary supplement in pill form. Always talk with your health care provider before starting L-theanine, especially if you are pregnant, breastfeeding, or taking other medications, as it may interact with some drugs.

What does theanine do to the body?

L-theanine may offer several health effects that can promote overall well-being, including mental alertness, enhanced relaxation, better sleep quality, reduced stress, and potential ADHD support. 

What is L-theanine best for?

L-theanine may work best for reducing stress and anxiety, as well as improving sleep quality. 

Is it safe to take theanine every day?

Yes, it is safe to take L-theanine every day. It is generally considered safe, with a recommended daily dose of 200-500 mg for healthy adults. 

Does L-theanine make you sleepy?

L-theanine doesn’t directly make you sleepy, but it may help you sleep better and for longer periods, especially when combined with GABA, which is known for its calming effects. 

Is L-theanine safe for kidneys?

Research on L-theanine being safe for kidneys is limited. A small study showed that high-doses of L-theanine reduced kidney and liver damage from sepsis. Talk with your health care provider if you have concerns or are on medications that affect kidney function. 

Which is better, L-theanine or ashwagandha?

Neither L-theanine nor ashwagandha is necessarily better than the other; both work to reduce anxiety and stress. It’s important to talk with your health care provider to find the best option for your needs.