increases serotonin, dopamine and glycine levels in various areas of the brain, as well as BDNF and NGF levels in certain brain areas. However, its effect on serotonin is still a matter of debate in the scientific community, with studies showing increases and decreases in brain serotonin levels using similar experimental protocols. It has also been found that injecting spontaneously hypertensive mice with theanine significantly lowered levels of 5-hydroxyindoles in the brain. Researchers also speculate that it may inhibit glutamate excitotoxicity. Effects A 2014 Natural Standard monograph that reviewed research on theanine reports that it is likely safe in doses of 200–250 mg up to a maximum daily dose of 1,200 mg. Natural Standard rates the evidence to support the usage of theanine for anxiety reduction, blood pressure control, and mood improvement as "unclear or conflicting scientific evidence" and the evidence for improved cognition as "fair negative scientific evidence". Many of the studies of theanine were done in combination with caffeine as found in tea. While the studies found that the combination had some effect on mood, the studies found that theanine alone had little effect. However a review by other researchers of a small set of trials concluded that there are benefits of L-theanine in reducing acute stress and anxiety in people with stressful conditions. and other subsequent studies have also concluded that it has an effect on reducing anxiety. In 2011, the EFSA (European Food Safety Authority) intervened with a scientific opinion on the alleged properties of L-theanine (improvement of cognitive functions, alleviation of psychological stress, maintenance of normal sleep conditions, reduction of menstrual pain) and concluded that at present there is no scientific evidence of a cause-and-effect relationship between the intake of L-theanine and the indicated benefits. Supplement use A 2020 systematic review concluded that L-theanine supplementation between 200 and 400 mg per day may help reduce stress and anxiety acutely in people with acute stress, but there is insufficient evidence for treatment of chronic stress. It further concluded that longer term and larger clinical study is needed to clinically justify its use therapeutically. In 2003, the German Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung, BfR) objected to the addition of isolated theanine to beverages. The institute stated the amount of theanine consumed by regular drinkers of tea or coffee is virtually impossible to determine. While it was estimated the quantity of green tea consumed by