Minor nootropic effect aside, nicotine is absolutely terrible for the human body. Most people don't realize this because public health campaigns highlighting issues with tobacco products include statements about negative health outcomes caused by nicotine, but neglect to separate these issues from those that are linked to tobacco specifically.
Nicotine consumption is linked to:
-accelerated tumor growth: https://www.nature.com/articles/nm0701_833
-vascular calcification: https://onlinelibrary.wiley.com/doi/abs/10.1111/eci.13077
-arteriosclerosis: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4805015/
-mutagenesis/various cancers: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4363846/
-reduced alveolar function and bronchoconstriction, miscellaneous pulmonary injury: https://pubmed.ncbi.nlm.nih.gov/3097432/; https://journals.physiology.org/doi/full/10.1152/ajplung.005...
-peridontal disease: https://onlinelibrary.wiley.com/doi/abs/10.1111/omi.12228