Although sold as a dietary supplement in the United States, Health Canada has not approved melatonin for sale in Canada.
http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20050720/melatonin_breastcancer_050719?s_name=&no_ads=
http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20050720/melatonin_breastcancer_050719?s_name=&no_ads=