Other activators of the dopamine reward system include opiates, amphetamines, and cocaine. Nicotine is 10 times more potent than heroin in its addictive properties. Symptoms can develop within hours of smoking last cigarette and can last for weeks.
Withdrawal is often worse in the evening.
Weight gain may occur. The biochemistry of nicotine is complex mainly because the part of the nervous system called the sympathetic system has receptor sites that interact with nicotine and are called nicotininc receptors . Another subset of receptors are called muscarinic receptors . Over time as a smoker keeps giving the body nicotine, the body learns to adapt to the extra stimulation by modifying the number of receptors and by decreasing production of the chemicals the body produces that would naturally stimulate these receptors. This is why new smokers feel ill but then develop tolerance to nicotine.