What it's normally used for
L-Tryptophan is an needed amino acid that the body uses to make proteins and brain-signaling chemicals.
Your body turns L-Tryptophan into serotonin, which helps control your mood and sleep.
Low levels of L-Tryptophan might cause depression. Some people take 1 to 3 grams of L-tryptophan a day to help improve mood or ward off mental health disorders like bipolar disorder, depression, or obsessive-compulsive disorder.
Taking L-Tryptophan before bed can help you go to sleep. Even doses as small as 250 milligrams can increase the quality of sleep, by making you spend more time in the deepest stage of sleep.
What it does for Lucid Dreaming
The body transforms L-Tryptophan into 5-HTP which converts to serotonin, melatonin, niacin, and auxins. Serotonin and Melatonin affect our dreams, and the quality of our sleep. L-Tryptophan also makes you spend more time in the deep stage of sleep, giving you REM rebound later on.
My own results
I take L-Tryptophan before bed and I remember more of the dream, where it seems like it's a longer dream.