Editing Tryptophan (section)

===Depression===
Because tryptophan is converted into [[5-hydroxytryptophan]] (5-HTP) which is then converted into the neurotransmitter serotonin, it has been proposed that consumption of tryptophan or 5-HTP may improve depression symptoms by increasing the level of serotonin in the brain. Tryptophan is sold [[over the counter]] in the [[United States]] (after being [[#Showa Denko contamination scandal|banned to varying extents between 1989 and 2005]]) and the [[United Kingdom]] as a [[dietary supplement]] for use as an [[antidepressant]], [[anxiolytic]], and [[sleep aid]]. It is also marketed as a [[prescription drug]] in some European countries for the treatment of [[major depression]]. There is evidence that blood tryptophan levels are unlikely to be altered by changing the diet,<ref name="DOI10.1111/j.1601-5215.2010.00508.x">{{cite journal | vauthors = Soh NL, Walter GT | title = Tryptophan and depression: can diet alone be the answer? | journal = Acta Neuropsychiatrica | volume = 23 | issue = 1 | pages = 1601–5215 | year = 2011 | doi = 10.1111/j.1601-5215.2010.00508.x | s2cid = 145779393 }}</ref><ref name="Fernstrom">{{cite journal|vauthors=Fernstrom JD|date=2012|title=Effects and side effects associated with the non-nutritional use of tryptophan by humans|journal=The Journal of Nutrition|volume=142|issue=12|pages=2236S–2244S|doi=10.3945/jn.111.157065|pmid=23077193|doi-access=free}}</ref> but consuming purified tryptophan increases the serotonin level in the brain, whereas eating foods containing tryptophan does not.<ref name="Wurtman_1980">{{cite journal|vauthors=Wurtman RJ, Hefti F, Melamed E|date=1980|title=Precursor control of neurotransmitter synthesis|journal=Pharmacological Reviews|volume=32|issue=4|pages=315–35|doi=10.1016/S0031-6997(25)06841-3 |pmid=6115400}}</ref>

In 2001 a [[Cochrane review]] of the effect of 5-HTP and tryptophan on depression was published. The authors included only studies of a high rigor and included both 5-HTP and tryptophan in their review because of the limited data on either. Of 108 studies of 5-HTP and tryptophan on depression published between 1966 and 2000, only two met the authors' quality standards for inclusion, totaling 64 study participants. The substances were more effective than [[placebo]] in the two studies included but the authors state that "the evidence was of insufficient quality to be conclusive" and note that "because alternative antidepressants exist which have been proven to be effective and safe, the clinical usefulness of 5-HTP and tryptophan is limited at present".<ref name="pmid11687048">{{cite journal | vauthors = Shaw K, Turner J, Del Mar C | title = Tryptophan and 5-hydroxytryptophan for depression | journal = The Cochrane Database of Systematic Reviews | issue = 1 | pages = CD003198 | year = 2002 | volume = 2010 | pmid = 11869656 | doi = 10.1002/14651858.CD003198 | editor1-last = Shaw | editor1-first = Kelly A | url = https://espace.library.uq.edu.au/view/UQ:209937/UQ209937_OA.pdf }}</ref> The use of tryptophan as an [[adjuvant therapy|adjunctive therapy]] in addition to standard treatment for mood and anxiety disorders is not supported by the scientific evidence.<ref name=pmid11687048/><ref name=Ravindran>{{cite journal | vauthors = Ravindran AV, da Silva TL | title = Complementary and alternative therapies as add-on to pharmacotherapy for mood and anxiety disorders: a systematic review | journal = Journal of Affective Disorders | volume = 150 | issue = 3 | pages = 707–19 | date = September 2013 | pmid = 23769610 | doi = 10.1016/j.jad.2013.05.042 }}</ref>