Smoking cessation withdrawal symptoms generally include smoking cravings, anxiety, and depression. Smokers suffer from both physical and psychological dependence. Physical dependence manifests itself in a series of intolerable withdrawal reactions that occur when the amount of smoking is reduced or when smoking stops, including craving for smoking, anxiety, depression, lack of concentration, headache, increased salivary gland secretion, and sleep disorders. Psychological dependence, also called mental dependence, is often characterized by a strong subjective craving for smoking. If a tobacco addict chooses to smoke again after experiencing withdrawal symptoms, it will reduce or eliminate withdrawal symptoms and disrupt the process of quitting. In general, withdrawal symptoms are strongest 14 days before quitting, can begin hours after quitting, and then gradually decrease until they disappear. Most withdrawal symptoms last up to about a month, and some cravings last more than a year.