Essential amino acid that is not produced by the body and must be taken from the diet.It is naturally found in many proteins of animal and plant origin (eggs, milk, cheese, soy, marine fish, nuts).It is a precursor of serotonin (George 1989, Yurcheshen 2015) through its metabolite 5-HTP or Oxitriptan (see card) and is credited with antioxidant properties (Tsopmo 2009).There is no conclusive scientific evidence that tryptophan supplements are effective on depression, insomnia, attention deficit, other diseases or improvement of physical performance (Yurcheshen 2015).It has been associated to a serious outbreak of Eosinophilia-Myalgia Syndrome with more than 1,500 cases and 37 deaths occurring in the 1990s, possibly caused by contaminated or poorly prepared batches of tryptophan (Falk 2011, Allen 2011, Sachs 2013, Yurcheshen 2015, Mediine Plus 2015). The FDA has launched a precautionary measure by withdrawing it from the market for years. At high doses it may cause side effects that are harmful to health (Fernstrom 2012). Tryptophan is a natural component of breast milk, with higher concentration in colostrum than in mature milk (Zarando 1989, Kamimura 1991) which is believed to have a circadian rhythm that regulates the sleep pattern and behavior of the infant ( Heine 1995, Cubero 2005).By taking tryptophan or alpha-lactalbumin (a high tryptophan-containing protein) tryptophan levels in breast milk is not increased (Dowlati 2015), but plasma prolactin concentration doest it (Chaney 1982, Cowen 1985) . With a comprehensive diet, tryptophan supplements are not needed at all, as their effectiveness has not been proven yet in any disease or disorder.Whenever used, a moderate consumption is recommended, making sure a reliable source since poisoning has been reported in the past.