Introduction: Tobacco dependence is a cluster of behavioural, cognitive, and physiological phenomena. We aimed to investigate the changes in the hematological parameters, lipid profile and depressive symptoms before and after smoking cessation. Methods: In this intervention study, 150 cases admitted to the clinic to quit smoking and stopped smoking for at least three months were investigated. All participants have received motivational interview and appropriate medical treatment (varenicline, bupropion, nicotine replacement therapy). We designed the study to evaluate the effects of cigarette smoking on some biochemical markers and depressive symptoms. Results: Motivational interviews were conducted on all participants, and 68,7% (n = 103) were treated with varenicline, 19,3% (n=29) with bupropion and 12% (n=18) with nicotine replacement therapy (NRT). There was a statistically significant relationship between the treatment method and the smoking cessation duration (p=0.002). Cessation period was longer in the group using varenicline. After quitting smoking, the Beck Depression Scores (BDS) decreased significantly (p<0.001). In cases with smoking duration between 3-6 months, the levels of carbon monoxide (CO) (p<0.001), white blood count (WBC) (p<0.001), hematocrit (p=0.003), hemoglobin (Hb) (p=0.002) and mean corpuscular volume (MCV) (p<0.001) decreased significantly. Conclusions: In our study, positive changes were observed in hematologic, biochemical parameters and depressive symptoms after quitting smoking. So, it is important that the society should be informed about the dangers of smoking. In particular, primary health care physicians should ask each patient whether they smoke or not, and encourage to quit smoking.