What are the withdrawl symptoms of quitting smoking for an adult?

Variety: Typical symptoms include tremor, fast heart rate, changes in mood, anxiety and agitation.

Many: Nicotine exploits brain signals associated 'reward'' and feeling 'safe/secure'. This is the same primitive signal we feel with many positive experiences; food when hungry, new love, or even sex activate the same signal. Taking that signal away is very unpleasant. Stopping nicotine leads to the opposite, loss of a sense of security (anxiety), fear, irritability, and eliminates the 'reward' signals.