What Is L-Tryptophan?
Tryptophan is a precursor to serotonin and melatonin and is an essential amino acid, meaning that the body cannot naturally produce it and so it must be attained through food or supplementation.  While foods such as turkey, cheese, chicken, bananas, milk, fish, tree nuts, and tofu contain high amounts of tryptophan, other compounds within the food may interfere with the absorption of tryptophan, making supplementation a good choice for those looking to benefit from stronger effects. 
Sleep Benefits of Tryptophan
Tryptophan is a precursor to melatonin and so can aid in improving sleep quality. One study found that tryptophan supplementation decreased sleep latency and slightly increased sleeping time.  The greatest effects are felt by those who have longer-than-average sleep latency times.  It is thought that tryptophan brings on sleep by raising levels of serotonin in the brain. Not only can tryptophan help those unable to fall asleep, it can also help those unable to wake up. A study found that taking tryptophan before going to bed can also improve alertness upon waking in the morning. 
Tryptophan Supplements and Serotonin
Since tryptophan is a precursor to serotonin, it can be used to improve mood.  It is usually used in combination with pyridoxine and ascorbic acid, both of which are involved in tryptophanâ€™s metabolism to serotonin.  Serotonin is a neurotransmitter that transmits signals between cells; changes in the level of serotonin in the brain can alter mood. A couple studies show that a combination of 5 Hydroxytryptophan (5-HTP) and Tryptophan can also help to improve mood. 
Tryptophan Side Effects
Reported side effects include heartburn, stomach pain, gas, vomiting, diarrhea, and loss of appetite.
The recommended dosage is 500mg daily. To increase absorption rate, take with a food or beverage high in carbohydrates, but avoid foods high in protein. Carbohydrate intake releases more insulin which decreases the amount of other amino acids but does not decrease tryptophan, while proteins contain additional amino acids that compete with tryptophan for entry into the brain.