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. 2008 Jul 2;3(7):e2544. doi: 10.1371/journal.pone.0002544

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This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

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Where applicable, respondents were asked to specify if the product was primarily used as a medicine, or as a health tonic. In this study we define medicine as a substance used to cure an illness, while a tonic is a substance used to primarily to promote general health and well being.