BACKGROUND:Historically, smoking cessation was thought to negatively impact substance use outcomes among smokers who use other substances. We sought to synthesize recent reports on this association. METHODS:Google Scholar, PubMed, and Cinahl were searched for studies published from 2006 to March 29, 2016 that reported impact of smoking cessation treatment or quitting smoking on substance use or substance use disorder treatment outcomes in the general population and among those in substance abuse treatment. Studies were grouped by reported impact as follows: "positive" (i.e. improved), "null" (i.e. no change), or "negative" (i.e. worsened). RESULTS:Twenty-four studies were included. Eighteen reported the impact of quitting smoking and six reported the impact of smoking cessation treatment intervention, independent of quitting, on substance use outcomes. Eleven studies (46%) reported solely positive impact; four (17%) reported solely null impact; eight (33%) reported mixed positive and null impact by analysis (combined and subgroup, n=1); substance (n=4); length of follow-up (n=2); and comparison group (n=1). One study (4%) reported mixed negative and null impact by ethnic group. No studies reported increased substance use. CONCLUSION:Smoking cessation does not appear to have a negative effect, and often has a positive effect on substance use outcomes. Smoking cessation advice should be offered, without hesitation, to smokers who report substance use and those in treatment for substance use disorder.