Though the names are similar, L-theanine and Magnesium L-Threonate are two different supplements. L-theanine, as we've discussed, is an amino acid often found in green tea, while Magnesium L-Threonate is a form of the mineral magnesium.  However, both are linked to improved brain health and their ability to cross the blood-brain barrier. Both are often used to improve symptoms of ADHD.