L-theanine supplements are a popular choice among those looking for natural stress management. L-theanine is a unique amino acid that comes from green tea that delivers antioxidant properties and helps promote healthy relaxation without drowsiness or any side effects associated with other options. It also promotes a healthy heart and cardiovascular function with this same relaxing effect. L-theanine closely resembles another amino acid, glutamic acid, which is a neurotransmitter in the brain. Overall, L-theanine is best known for its anti-stress benefits. Read some of the reviews on the products below to see how they may help you fight the negative effects of stress.