Theanine is calming. For example, pure theanine and magnesium are the only two substances Huberman recommends as sleep aids.
There is a minor complication in which if the brain is in a very stimulated state, then theanine can add to the stimulation, but that has happened to me only once in hundreds of times of my using theanine at bed time, and is extremely unlikely to recur now that I know about the complication.
