Theanine is an amino acid that’s found in green tea and green-tea extract. It’s the dominant amino in tea plants, and it’s what gives green tea its slightly sweet taste. While green tea has other ingredients that confer multiple health and training benefits, theanine is particularly great for boosting focus and relaxation. It helps with recovery from training, and it also helps the body recover from excitatory substances like caffeine. This lets you use caffeine as an energy booster without worrying about the effects hanging around longer than you’d like. Theanine is also available as a stand-alone ingredient, which is ideal if you’re using it for its relaxation properties. But keep in mind, though, that research shows a better brain boost when theanine and caffeine are combined than when theanine is taken alone.