Nicotine

Acute use causes transient increases in heart rate, blood pressure, and systemic vasoconstriction including coronary arteries;citation needed long-term exposure may impair endothelial function and potentially contribute to atherosclerosis, with cardiac arrhythmias primarily a concern in individuals with underlying heart disease. Short-term nicotine use in healthy individuals poses little cardiovascular risk.

Heavy chronic use is associated with less efficient brain network architecture and disruptions in topological organization of brain networks; adolescent exposure may impair neurodevelopment up to age twenty-five,citation needed and some research suggests potential damage to medial habenula neurons regulating nicotine avoidance behaviors in chronic users.

Nicotine is considered a possible teratogen in humans; it crosses the placenta and negatively affects fetal brain development, with prenatal exposure associated with lower birth weight, increased risk of miscarriage and stillbirth, and potential long-term metabolic and neurobehavioral consequences in offspring.citation needed

Chronic exposure suppresses both innate and adaptive immune responses, downregulating cell-mediated immunity against infections and potentially reducing immune surveillance against neoplastic diseases.citation needed

May promote and aggravate periodontal diseases including periodontitis and gingivitis, particularly in the presence of harmful oral microorganisms.