People with substance use disorders (SUD) have a high prevalence and rate of smoking with little success in quitting, so stronger approaches are needed to encourage attempts to quit smoking. Brief advice (BA), to motivate cessation, produced some benefit but low abstinence rates for smokers with SUDs while adding free transdermal nicotine replacement therapy (NRT) improved short-term cessation rates. Varenicline has been found to produce higher rates of short and long-term abstinence than bupropion or placebo. However, a comparison between the efficacy of varenicline and NRT has not yet conducted with people with SUDs. Given the lack of effectiveness for standard smoking treatments for this population, what needs to be known is whether varenicline would increase the smoking abstinence rates relative to NRT when all receive motivational counseling.