L-theanine is an amino acid derived from green tea leaves, explains WebMD. Although clinical studies are sparse, L-theanine may treat high blood pressure, prevent dementia and increase the efficacy of cancer drugs. It also may help people to relax without causing drowsiness, reports Drugs.com.
Because L-theanine appears to lower blood pressure, WebMD warns that using it along with medications that treat high blood pressure may cause blood pressure to dip too low. Stimulant medications, which speed up the nervous system, may also be less effective when taken in conjunction with L-theanine because the amino acid seems to slow down the nervous system.