There are a lot of topics already discussing this; you'll find you can get your information quicker if you look for them (under lucid aids sub forum!).
Originally Posted by Konfusi0n
Anyways, in the circadian rhythm, there are 2 hormones that play a factor; Melatonin and Serotonin. Melatonin acts as your 'lights off' hormone, where as Serotonin acts as your 'lights on' hormone. Basically, serotonin keeps you awake and active, where as melatonin makes you go to sleep.
Melatonin induces deep sleep (Stages 1-4), and inhibits REM sleep. Serotonin will do the opposite effect for your sleep, as well is needed for the logical / critical thinking section of your brain to fully function.
The 2 are naturally balanced in the common person, but one will be in abundance over the other at different times of the day. During the day, serotonin will peak, and at night, melatonin will peak. Light induces the secretion of serotonin, where darkness induces melatonin.
In our sleep cycles, we are required to get a certain amount of REM sleep. Lack of REM sleep has been proven to eventually lead to death; its quite an important! However, melatonin inhibits REM sleep, causing you to have less REM and more deep sleep.
But since your body needs the REM sleep, it will have to make up for the time it lost when melatonin was in abundance (I think this is why our REM cycles get longer at night, not too sure). What happens when you take a melatonin supplement is you are causing an excess amount of melatonin into your brain, causing you to have less REM sleep early in the night, but once the excess amount goes away, your brain will start to catch up with REM sleep, causing you to have longer REM sleep cycles later in your sleep (early morning).
The benefit of this is that during the early hours of our sleep, we are so tired and groggy that when we do have REM sleep, we don't even recognize that we are dreaming. However, if we take the melatonin supplement, our REM sleep will be shorter in these 'groggy' periods, and a lot longer in our more awake periods. This will allow us to dream longer and more intensly when we are more aware in the morning, hence making it easy to become aware while dreaming.
Take the melatonin as you goto bed. It doesn't take a lot of melatonin; I would recommend no more than 1 3mg pill (this is what I use). This will cause the later REM cycles to grow longer.
An REM rebound helps dreaming as we dream most vividly in REM sleep. During REM sleep, our brainwaves are the closest to when we are awake, which creates the life like dreams that we have. Since we can achieve longer REM sleep later in the morning, we will be more refreshed and capable to recognize we are dreaming, as well as have longer dreams to lucid dream in.
Melatonin will increase vividness, but it can hinder recall. In the dose you are taking, you will not see any affect on recall (well, you'll remember the dreams better as they'll be super vivid). However, certain drugs suchs as marijuana cause massive amounts of melatonin to secrete into the brain. This is the reason why most users do not remember their dreams at all, and wake up groggy if they're constant users.
TL;DR, 3mg, makes your dreams longer.