L-theanine, an amino acid found in green and black tea leaves, is a popular supplement often used to support sleep. Taking it nightly could help your body calm down and appears to pose little short-term risk for most people, though its long-term effects aren’t clear.
For some people, taking L-theanine regularly may improve overall sleep quality. Unlike some sleep aids, L-theanine doesn’t “knock you out,” said board-certified sleep medicine physician Andrea Matsumura, MD, FACP, FAASM.
Instead, within about 40 minutes of taking it, L-theanine crosses the blood-brain barrier and can help calm the nervous system, lowering heart rate and blood pressure. It may also reduce levels of the stress hormone cortisol and promote slower brain wave activity associated with relaxation.
If you take L-theanine nightly, you may reap these benefits with little short-term risk. Taking the supplement every night is generally considered safe and is unlikely to cause dependency or rebound insomnia, said John Rinker, MD, an internal medicine physician at OSF HealthCare.
Still, research is mixed on the supplement’s long-term effects and ideal dosage, so experts caution against habitual use. It’s best to consult a physician before taking L-theanine routinely, and to keep in mind that it should be used as a way to support sleep, not as a replacement for good sleep habits, said William Lu, MD, sleep expert and director at Sunrise.
L-theanine may be a good choice for people with nighttime anxiety or mild insomnia, Rinker said. If you have trouble falling or staying asleep at least three nights a week for three months or longer, you might have chronic insomnia, which often requires more intensive treatment.
Some people should be cautious about taking it or avoid it altogether, experts said. This includes children and adults who are:
A typical dose of L-theanine is about 100 to 200 milligrams once or twice daily, said Rinker. Most people, however, take 200 milligrams 30 to 60 minutes before bed.
Matsumura cautioned against exceeding 400 milligrams per day, noting that higher doses could cause side effects like headaches or nausea. Start slow and increase only if needed, she recommended.
Because most supplements aren’t regulated in the United States, Rinker suggested choosing a product that’s been third-party tested for purity and label accuracy by organizations like the National Sanitation Foundation (NSF).
