Brain & Central nervous System– Nicotine is known to be a stimulant for the brain. On reaching the CNS, it gives an initial energy boost. After sometime, when the effect reduces it gives you crave for more. It gives you good feeling when you are smoking, but it can make you anxious, nervous, moody and depressed afterwards. It is also known to increase the risk of muscular degeneration, cataracts and poor eye sight.