Brain Magnesium with Magtein® from Doctor's Best® features Magtein-brand magnesium l-threonate. Each bottle contains 30 servings with each serving of three capsules containing 2,084 mg of Magtein. Magnesium is essential for the brain connections (synapses) that facilitate learning, memory, attention and all other brain functions. The l-threonate salt extends the action of magnesium.