L-Theanine

Theanine or l-theanine, is an amino acid found in the leaves of Camellia sinesis, better known as green tea. So apart from the anti-oxidant benefits of green tea, the theanine in green tea, offers an anti-stress benefit as well.

Theanine is unique, in that it acts as a non-sedating relaxant by increasing the brain's production of alpha waves.

So in fact, it is very effective in helping to relieve tension, stress and anxiety, without causing drowsiness, except I find,in the evening when I'm already drowsy and am fighting it or too stressed to relax enough to allow myself to fall asleep, it does help me sleep.

As well as being relaxing, it has also  been shown to promote concentration (in students), by increasing alpha waves in the brain.

Theanine has been shown to effective in dosages ranging from 50-200mg a day. Three to four cups of tea would usually contain about 100-200mg of theanine, which counteract the stimulant effects of caffeine. Unfortunately decaffeinating green tea also loses theanine.

If you want to avoid caffeine or have a more reliable source of theanine, theanine comes in capsule and tablet form.
It reaches maximum peak blood levels about 30 mins to 2 hours after ingestion, so it can be used as needed in the day and regularly at night.

One to two 100mg capsules at night are usually sufficient.
If you're stressed or need to focus or concentrate more in the day, take half a capsule,  or you can get 50mg capsules as well, of l-theanine.