Passionflower is also a very good sleep aid in the right quantities.

It amplifies the effects of melatonin.

The combination of passionflower and melatonin is one of the best remedies for sleeplesness since it not only works very well, but unlike most other substances that work this well, you don't devellop tolerance to it, it's not addictive and it has no after effects like a hangover or drowsyness in the morning.

Many other sleep aids also prevent deep REM-sleep. Especially alcohol, and benzodiazepines that many people use as sleep-aid have this effect.

Alcohol and valium are both (as far as i know) GABA-agonists so this could very well aply to other GABA-agonists like L-theanine as well.