Tryptophan is an amino acid-one of the building blocks found in proteins. When you break down proteins in your meal with hydrochloric acid in your stomach,the amino acids are used as building blocks by your body to make many things. Good quality hair,skin,nails,and muscles are all dependent on adequate protein break-down and amino acid absorption. Neurotransmitters are also made from amino acid building blocks. Serotonin is a neurotransmitter associated with mood. Low levels of serotonin are associated with depression/anxiety. The brain can use tryptophan to restore serotonin levels to normal,reducing the need for prescription drugs. Most of the time,depression not associated with external circumstances, is due to some deficiency: Thyroid hormone,progesterone,vitamin D3,magnesium,tryptophan and tyrosine are deficiencies commonly associated with depression. The books "The Mood Cure" By Julia Ross and "The Thyroid Solution" by Ridha Arem MD are books to read to take control of depression and other mood disorders and get off drugs. Antidepressants should be weaned off gradually under the supervision of a professional. Tryptophan is also a beneficial sleep aid. 1,000-2,000 mg at bedtime will usually improve sleep by allowing the brain to make more of the sleep hormone-melatonin.