Can L-Theanine Cause Headaches or Migraines?

Quick answer: Yes, L-theanine can cause headaches in some people, though it's not a common side effect. In research, headaches were more likely when L-theanine was taken on its own, and less likely when it was taken with caffeine. Migraines have also been reported, but are rare. For most people, L-theanine is well tolerated. If it gives you headaches, they usually go away after you stop taking it.

L-theanine is a common supplement people use for relaxation, sleep, and focus. It's considered gentle and easy to tolerate. This amino acid is found in green tea, but supplements usually provide higher amounts than tea and often without the caffeine it contains. 

Some people get headaches after taking L-theanine, and a few report migraines. If you notice these effects, you're not imagining them.

This article covers what research says about L-theanine and headaches, why some people are affected, and what you can do if you get headaches.

What Is L-Theanine?

L-theanine is an amino acid mostly found in green tea and some mushrooms. People take it as a supplement to relax, reduce stress, improve focus, and sleep better. It works by influencing brain chemicals that help you feel calm and alert, such as GABA, serotonin, and dopamine.

Most studies use doses of 200 to 400 mg per day, and L-theanine is usually considered safe. Clinical trials have not found serious side effects, even with higher doses. Still, some people do get headaches after taking it.

Can L-Theanine Cause Headaches?

Yes, but it's not common. In a 2008 study, researchers tested L-theanine, caffeine, and the two together. People who took L-theanine on its own reported higher headache ratings than those who didn't.

A more recent review found that L-theanine is generally well tolerated, and that when side effects do happen, headache, migraine, and digestive problems are the most common. So headaches are a recognized side effect, but they affect only some people, and most users have no trouble.

Headaches seem more likely when you first start taking L-theanine or when you take a higher dose. For many people, they fade as the body adjusts or after stopping the supplement.

Also Read: This Common Habit Makes Insomnia Worse 

Can L-Theanine Cause Migraines?

Some people have reported severe headaches or migraines after taking L-theanine, though this appears to be rare. Most L-theanine research reports general headaches rather than migraines specifically, so the migraine link is based more on individual reports than on clinical studies.

If you often get migraines, L-theanine could possibly trigger one, especially at a higher dose. This may be related to how L-theanine widens blood vessels, which is explained in the next section.

If you get a migraine after starting L-theanine, stop taking it and talk to your doctor before using it again.

Why Does L-Theanine Cause Headaches in Some People?

L-theanine may cause headaches because of how it affects your blood vessels. It acts as a vasodilator, which means it widens blood vessels. L-theanine increases nitric oxide, a molecule that helps relax and open blood vessels. Research shows L-theanine boosts nitric oxide through a pathway called eNOS, which is also why it can lower blood pressure slightly.

When blood vessels in the head widen, it can trigger headaches and migraines. This is similar to how some vasodilator medications can cause headaches. So if you're sensitive to this effect, L-theanine may give you a mild headache.

Everyone reacts to L-theanine differently because of their body chemistry. This is probably why some people get headaches, and most do not. The dose matters too, since higher amounts are more likely to cause side effects.

Does Caffeine Make L-Theanine Headaches Better or Worse?

In the 2008 study, people who took L-theanine alone had more headaches, but those who took it with caffeine actually had fewer headaches.

People often take L-theanine in different ways. In green tea, L-theanine and caffeine are both present.  However, many sleep supplements contain only L-theanine without caffeine. Research shows that headaches are more likely when people take L-theanine alone.

However, caffeine can make it harder to sleep if you take it near bedtime, so adding caffeine is not a good idea if you use L-theanine to help you rest. Some people also get a racing or pounding heartbeat from caffeine.

If you take L-theanine with coffee or another source of caffeine and notice heart palpitations, lower your caffeine intake and talk to your doctor.

Also Read: 10 Inflammatory Foods That Can Disrupt Your Sleep

Do L-Theanine Headaches Go Away?

For most people, yes. L-theanine headaches often fade within a few days as your body gets used to the supplement. If they don't, stopping L-theanine usually resolves them. Because L-theanine leaves your body within hours, headaches caused by it tend to ease fairly quickly after you stop.

If your headaches continue even after you stop taking L-theanine, something else is likely causing them, and it's worth seeing a doctor.

Other Side Effects of L-Theanine

Headaches are not the only side effect some people notice. Most people tolerate L-theanine well, but others have reported side effects, including:

• Dizziness, usually with higher doses.

• Nausea or stomach upset, more likely on an empty stomach.

• Drowsiness, which is expected given its calming effect, can be unwanted during the day.

• Lower blood pressure, which may be a concern if your blood pressure already runs low.

Taking L-theanine with food can reduce the chance of nausea. As with any supplement, lower doses are less likely to cause side effects.

Who Should Be Careful With L-Theanine?

L-theanine is usually safe, and the FDA says it is "generally recognized as safe." However, some people should be extra careful or avoid it.

Because L-theanine can lower blood pressure, it may interact with certain medications and supplements, including:

• Blood pressure medications, since the effects can add up

• Other supplements that lower blood pressure

• Stimulant medications, such as those used for ADHD

• Caffeine supplements 

If you take any of these, talk to your doctor before using L-theanine. People who are pregnant or nursing should avoid L-theanine, since there isn't enough research to confirm it's safe during these times.

Does L-Theanine Help With Migraines?

Some people take L-theanine hoping it will help with migraines, since it has a calming effect and may ease stress, which is a common migraine trigger. However, the evidence supporting this use is limited, and L-theanine is not a proven treatment for migraines.

In some cases, it can even cause headaches for some people, making it an unreliable choice for migraine relief. If you frequently experience migraines, it’s important to see a doctor for help with finding the right treatments.

What to Do If L-Theanine Gives You Headaches

If you think L-theanine is causing your headaches, a few steps can help:

• Lower your dose. Side effects are more likely at higher amounts, so a smaller dose may help.

• Take it with food. This won't stop headaches, but it can reduce nausea that sometimes comes with them.

• Stop and see if they go away. If your headaches clear after stopping, L-theanine was likely the cause.

• Talk to your doctor, especially if headaches are severe, turn into migraines, or come with other symptoms.

If L-theanine doesn't work for you, there are other natural sleep aids available that don't contain L-theanine and can help you achieve a good night's rest.

A melatonin-free, L-theanine-free alternative for sleep

If L-theanine causes headaches for you and you want another way to relax, try Sip2Sleep®. This liquid sleep aid does not contain melatonin. It uses Montmorency tart cherry extract and Rafuma leaf (Venetron®) to help you sleep naturally. Unlike L-theanine, it won’t leave you feeling groggy the next day. Always talk to your doctor before taking any supplement, especially if you are on other medications.

About the author

Dr. Ruchir P. Patel, MD, FACP, is the Medical Director of the Insomnia and Sleep Institute of Arizona and the founder of Sip2Sleep. He is triple board-certified in sleep medicine, obesity medicine, and internal medicine. Dr. Patel is a multi-year Phoenix Magazine Top Doctor and holds the Inspire Excellence designation.

References

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3. Dashwood R, Visioli F. l-theanine: From tea leaf to trending supplement - does the science match the hype for brain health and relaxation? Nutr Res. 2025 Feb;134:39-48. doi: 10.1016/j.nutres.2024.12.008. Epub 2025 Jan 2. PMID: 39854799; PMCID: PMC12892352. 

4. Dodd FL, Kennedy DO, Riby LM, Haskell-Ramsay CF. A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. Psychopharmacology (Berl). 2015 Jul;232(14):2563-76. doi: 10.1007/s00213-015-3895-0. Epub 2015 Mar 13. PMID: 25761837; PMCID: PMC4480845.