Nicotine is a psychoactive substance, that is, it acts on the brain through neurons and neurotransmitters. These then produce dopamine, a hormone that provides satisfaction.
By dint of repetition, the brain gets used to the presence of nicotine. And when consumption stops, a feeling of unease appears: the body is lacking nicotine. This lack can be expressed in different ways: strong cravings for smoking, nervousness, agitation, nervousness, anxiety, difficulty concentrating, sleeping ... When the brain is "replenished" nicotine, these signs disappear. This is why nicotine patches and chewing gums help neutralize the symptoms of nicotine withdrawal when you stop smoking. However they are not miraculous: they are not enough by themselves to carry out a stop of tobacco. Other dimensions of tobacco dependence are also to be taken into account.