Ever wonder why smokers crave a cigarette when they're in a bad mood or in a stressful situation? It's because nicotine may help people feel calmer, causing temporary feelings of relaxation as well as reducing stress, anxiety and even pain [source: World Health Organization].
In spite of that relaxation, though, nicotine actually increases physical stress; its effects are considered a bit of a paradox. It perks up the central nervous system, but depending on the dosage some smokers find nicotine also acts as a sedative. Some studies, though, suggest it may just be the ritual of smoking that induces a calming effect, because nicotine is actually considered a stimulant, not a depressant.
When you first inhale, nicotine causes your body to release the hormone epinephrine, which is the "fight or flight" hormone. Epinephrine activates the sympathetic nervous system, making your breathing become rapid and shallow, your heart rate increase, and your blood pressure rise. You're alert.
Nicotine can also lead to insulin sensitivity and insulin resistance, as well as an increased risk of developing metabolic syndrome, type 2 diabetes and cardiovascular disease. It affects thyroid hormones, pituitary hormones, sex hormones and adrenal hormones. Insulin resistance in cigarette smokers, for example, may be in part because nicotine stimulates the body to produce high levels of adrenal androgens -- in other words, nicotine impacts the body's glucose metabolism, leading to hyperglycemia and hyperglycemia associated with insulin resistance. Insulin resistance not only increases the risk of developing type 2 diabetes but also heart disease [source: Kapoor].