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. 2018 May 18;21(10):1310–1319. doi: 10.1093/ntr/nty101

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© The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 1. — PRISMA flowchart. Articles were retrieved from PubMed and Embase databases (n = 521) and via citation tracking (n = 2). Articles published between the year of 1990 and the search date (May 2017; updated in January 2018) were included.