Melatonin
<p ><b>Melatonin</b> <a href="http://upload.wikimedia.org/wikipedia/commons/5/5f/Melatonin-pronunciation.ogg" title="Listen" ><img src="/43e4e352-a267-5c8b-95b3-30bd67978c77.png"/></a><sup class="noexcerpt" ><a href="http://en.wikipedia.org/wiki/File:Melatonin-pronunciation.ogg" title="File:Melatonin-pronunciation.ogg" >i</a></sup><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Key" title="Wikipedia:IPA for English" >ˌmɛləˈtoʊnɪn</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a>, also known chemically as <b><i>N</i>-acetyl-5-methoxytryptamine</b>,<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-0" >[1]</a></sup> is a naturally occurring compound found in animals, plants, and microbes.<sup id="cite_ref-Caniato2003_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-Caniato2003-1" >[2]</a></sup><sup id="cite_ref-Paredes2009_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-Paredes2009-2" >[3]</a></sup> In animals, circulating levels of the
<a href="http://en.wikipedia.org/wiki/Hormone" title="Hormone" >hormone</a> melatonin vary in a daily cycle, thereby allowing the <a href="http://en.wikipedia.org/wiki/Entrainment_(chronobiology)" title="Entrainment (chronobiology)" >entrainment</a> of the <a href="http://en.wikipedia.org/wiki/Circadian_rhythm" title="Circadian rhythm" >circadian rhythms</a> of several biological functions.<sup id="cite_ref-Altun2007_3-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-Altun2007-3" >[4]</a></sup></p>
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Many biological effects of melatonin are produced through activation of <a href="http://en.wikipedia.org/wiki/Melatonin_receptor" title="Melatonin receptor" >melatonin receptors</a>,<sup id="cite_ref-Boutin2005_4-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-Boutin2005-4" >[5]</a></sup> while others are due to its role as a pervasive and powerful <a href="http://en.wikipedia.org/wiki/Antioxidant" title="Antioxidant" >antioxidant</a>,<sup id="cite_ref-Hardeland2005_5-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-Hardeland2005-5" >[6]</a></sup> with a particular role in the protection of <a href="http://en.wikipedia.org/wiki/Nuclear_DNA" title="Nuclear DNA" >nuclear</a> and <a href="http://en.wikipedia.org/wiki/Mitochondrial_DNA" title="Mitochondrial DNA" >mitochondrial DNA</a>.<sup id="cite_ref-Reiter2001_6-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-Reiter2001-6" >[7]</a></sup>
Products containing melatonin have been available <a href="http://en.wikipedia.org/wiki/Over-the-counter_drug" title="Over-the-counter drug" >over-the-counter</a> in the United States since the mid-1990s.<sup id="cite_ref-7" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-7" >[8]</a></sup> In many other countries, the sale of this <a href="http://en.wikipedia.org/wiki/Neurohormone" title="Neurohormone" >neurohormone</a> is not permitted or requires a prescription.</p>