**4. Adverse effects of smoking**

Cigarette smoke is a complex mixture of chemicals. It is believed that the reason why people smoke is due to the active ingredient in the tobacco, nicotine which acts as a stimulant and a relaxant through its effects on the central nervous system, adrenals and the sympathetic nervous system [42, 43]. When a cigarette is smoked, nicotine-rich blood passes from the lungs to the brain within seven seconds and immediately stimulates the release of many chemical messengers including acetylcholine, norepinephrine, epinephrine, vasopressin, arginine, dopamine, autocrine agents, and beta-endorphin [42, 43]. This release of neurotransmitters and hormones is responsible for most of the effects of nicotine. Nicotine appears to enhance concentration and memory due to the increase of acetylcholine. It also appears to enhance alertness due to the increases of acetylcholine and norepinephrine. Arousal is increased by the resultant elevated level of norepinephrine. Pain is reduced by the increases of acetylcholine and beta-endorphin. Anxiety is reduced by the increased beta-endorphin. Nicotine also extends the duration of positive effects of dopamine and increases sensitivity in brain reward systems [44, 45]. This is one of the key reasons why cigarette is very addictive.

Some smoke components, such as carbon monoxide (CO), hydrogen cyanide (HCN), and nitrogen oxides, are gases. Others, such as formaldehyde, acrolein, benzene, and certain N-nitrosamines, are volatile chemicals contained in the liquidvapour portion of the smoke aerosol. Still others, such as nicotine, phenol, polyaromatic hydrocarbons (PAHs), and certain tobacco-specific nitrosamines (TSNAs) are contained in the submicron-sized solid particles that are suspended in cigarette smoke. In view of this chemical complexity, cigarette smoke has been shown to have multiple and highly diverse effects on human health. These adverse effects have been documented in literature to involve every organ in the human body culminating in various cancers, chronic obstructive pulmonary airway disease to various cardiovascular diseases. It has also been linked with auditory problems [46] while in India and China it has been associated with increased prevalence in pulmonary tuberculosis [47].

The use of tobacco has been reported to be associated with increased chronic lung diseases, asthma, angina depression, arthritis, diabetes, hypertension and cerebrospinal accidents [45–51]. The adverse economic effect of tobacco smoking is huge [5, 52, 53]. In the United States, an estimated \$96 billion per annum were being incurred from tobacco use and related medical expenses due to loss of productivity and over \$2 billion would be saved annually from healthcare insurance if all smokers in the US were to quit smoking [54].
