A study published in the Current Developments in Nutrition Journal investigates the effects of L-theanine supplementation on stress and cognitive function. Researchers conducted a randomized, double-blind crossover study on adults with non-clinical psychiatric symptoms. They gave participants either a placebo or 200 milligrams of theanine for four weeks, followed by a two-week washout period, and then continued the crossover study (in which participants were switched treatments).

The researchers found that theanine supplementation led to significant decreases in stress and significant improvements in sleep quality and cognitive function compared to the placebo.

While more research is needed to elucidate the benefits of theanine in clinical populations, this supplement appears to be effective for reducing stress and improving brain function in the general population. This is likely enhanced when coupled with a healthy diet and lifestyle practices, such as meditation and regular exercise.