Hat tip to the first post in this thread, with a bit of clarification.
Wash your tea leaves for no longer than 20 s with very hot, but not quite boiling water. That will remove most of the caffeine, but leaves behind the theanine in the leaves.
When we learn to brew tea properly, one is ALWAYS taught to wash the tea leaves, regardless of technique origin (East or West). For this reason, constant imbibing of tea throughout the day doesn't impair sleep at night, even when tea is drunk in the evening hours.
Theanine imparts a 'mellow' feeling from tea consumption (Note: not all teas have it due to processing, leaf age or varietal/growing origin).
Theanine is our friend. It helps normalize release of serotonin and dopamine in the central nervous system. That is very good for inducing the types of brain waves we desire, ones that coordinate brain center activity and reduce stress hormone threshold level in response to chronic/daily stress. In other words, it conditions our CNS to accept higher levels of stress before firing off costly stress hormones.
Low dopamine = mild depression, compulsiveness and addictiveness, irritability, sleep disruption.
Most of us don't need the added kick of caffeine, but we do need that theanine, as well as the antioxidants in tea.
Now, you shouldn't waste money on expensive 'decaffeinated teas', because the
Swiss Hot Water' technique is essentially the same as our tea leaves wash. Some companies employ CO2-extraction, but that removes our theanine, so its not a wise choice. Certainly one should avoid organic solvent extracted teas because of their mildly toxic solvent contaminants in treated tea leaves. A little is no problem, but constant consumption isn't a good idea, as its counterintuitive (the antioxidant benefits of tea being negated by the solvent residuals).