What Happens to Your Sleep When You Take L-Theanine Every Day

L-theanine, an amino acid found in green and black tea leaves, is a popular supplement often used to promote sleep. Taking it every night might help your body calm down and appears to pose few short-term risks for most people, although its long-term effects are unclear.

For some people, taking L-theanine regularly may improve overall sleep quality. Unlike some sleep aids, L-theanine doesn’t “knock you out,” says board-certified sleep medicine physician Andrea Matsumura, MD, FACP, FAASM.

Instead, about 40 minutes after 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 a slowing of brain wave activity associated with relaxation.

If you take L-theanine every night, you can get these benefits with few short-term risks. Taking the supplement every night is generally considered safe and is unlikely to cause addiction 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, which is why experts caution against habitual use. It’s best to consult a doctor before taking L-theanine regularly and keep in mind that it should be used as a way to promote sleep, not as a replacement for good sleep habits, says William Lu, MD, a sleep expert and director of 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 three or more nights a week for three months or more, you may have chronic insomnia, which often requires more intensive treatment.

Some people should be careful or avoid taking it, experts say. This includes children and adults who are:

A typical dose of L-theanine is around 100 to 200 milligrams once or twice daily, Rinker said. However, most people 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 such as headaches or nausea. Start slowly and only increase if necessary, she recommended.

Since most supplements are unregulated in the United States, Rinker suggested choosing a product that has been tested for purity and label accuracy by organizations such as the National Sanitation Foundation (NSF).