Nicotine withdrawal involves irritability, headache, and craving. These symptoms happen with the sudden stopping or reduction of smoking (or other tobacco use) by a nicotine-dependent individual. See smoking - tips on how to quit and smoking hazards.
Almost all people who try to quit have some form of nicotine withdrawal. Generally, people who smoked longer or higher higher number of cigarettes are more likely to have withdrawal symptoms. The severity of the symptoms is also dependent on the duration of smoking and number of cigarettes smoked.
People who are regular smokers tend to have particularly strong cravings and worsening of withdrawal symptoms at certain times, places, or situations associated with smoking.
Anderson JE, Jorenby DE, Scott WJ, et al. Treating tobacco use and dependence: An evidence-based clinical practice guideline for tobacco cessation. Chest. 2002;121(3:932-941.
Fiore MC, Bailey WC, Cohen SJ, et al. Treating Tobacco Use and Dependence. Clinical Practice Guideline. Rockville, MD: US Department of Health and Human Services. Public Health Service. June 2000.