There are many articles and advertisements for so-called lucid aids and dreaming aids in the internet. I have tested a few so far. Some were quite useless or even counter-productive.
What has worked best for me so far is isolated soy protein.
This product caught my attention when there was a thread about it in the german lucid dreamers community Klartraumforum.de.
Isolated soy protein is full of amino acids which are precursors for diverse neurotransmitters.
I use one special brand of protein shakes: US-2 Xten Pro by US product line. This protein powder consists of pure protein with more or less no carbohydrates. I have tried several other powders by other brands so far (e.g. body attack) but I didn't like the taste and the consistency of the other powders so I stick to my brand.
Soy protein shakes have several advantages in comparison to common protein shakes based on casein, the milk protein:
Primary soy protein is absorbed much more quickly than casein, which remains a long time in the stomach.
A further advantage is the low carbohydrate content of the powder. Protein gives your brain REM sleep whereas carbohydrates open the blood brain barrier for Tryptophane, which makes you fall asleep quickly but facilitates deep non-REM-sleep.
When do I have to drink it?
According to my experience the optimal effect takes part after 4 to 5 hours after consuming. Ideal is drinking about 30 g during a short WBTB after 3 to 4 hours sleep.
I also had good results having a shake before bedtime. But you should not spend much time awake after having the shake as the big amount of some amino acids e.g. tyrosine will give you energy and you may have trouble falling asleep. Waiting to long may also delay your long REM phases to a time when the effect of the protein shake is already over.
Matcha: Green Tea
US Product Line Soja-Protein-Isolat at Amazon.de