The main risk factor is the number of cigarettes smoked over time. "Pack years" is a common measurement in medical lingo. Someone who smoked one pack per day for 15 years and then two packs per day for 20 years would have 55 pack years, which is fairly high; even 20 pack years will increase the risk of many chronic problems, chiefly lung disease (bronchitis and emphysema), lung cancer, and heart disease. Smokers have twice the risk of death prior to age 65 than nonsmokers, and there is an average reduced longevity of 5–10 years for smokers, varying from lighter to heavier users. For shorter-term problems, such as bronchitis, smoking more than 25 cigarettes per day is associated with a high risk and smoking between 10 and 25 per day with a moderate one; smoking fewer than 10 cigarettes daily poses a low risk. The length and depth of inhalations also contribute to nicotine and tar intake.

There are also different levels of addiction. Least addicted are those who smoke only socially—at parties with friends—and usually only during certain parts of the day or week. They may smoke primarily for psychosocial or image reasons. Next are those who smoke in response to stress, mainly at work. They may stop and start. These first two smoking types are usually less addicted than heavier smokers, and it is easier for them to cut down or stop. The third type of smoker is the more serious, all-day-long smokers who have a fairly strong physical and psychological addiction; for these people, going more than an hour without nicotine causes the onset of withdrawal symptoms, such as irritability, anxiety, or headache. Often, the psychological influences lead to more frequent smoking of cigarettes than even the physical needs require. The extreme, "graduate" level smoker is the "chain smoker." He or she puffs nearly constantly, usually consuming three packs or more a day, and is strongly addicted. The latter two types often need medical and psychological support unless some special circumstance or divine intervention motivates them to stop immediately. Specialized stop-smoking programs are often needed, and even these are only sometimes helpful. Currently, about a third of adult men and women smoke in the United States. Between 10 and 20 percent of previous smokers have quit, leaving only 40–50 percent of adults who have not been regular smokers, and even most of them have at least tried cigarettes. But now by popular demand, from medical and social support, over 1 million smokers of the 50 million in the United States are stopping yearly, and they will immediately begin to lower their cancer and cardiovascular disease risks as well as reduce the negative effects on their lungs and other tissues.

Contrary to current marketing hype about low-tar, low-nicotine cigarettes, there are no safe cigarettes. Some of the newer "lights" may be even worse than regular cigarettes. Users inhale more deeply and smoke more in order to is satisfy their nicotine needs. Unless they have a low ratio of tar to nicotine, there are more risks posed by the increased chemical tars in the cigarettes. More carbon monoxide, hydrogen cyanide, and nitrogen gases are consumed with many of these low-nicotine cigarettes, and this can increase the oxygen deficit, heart disease, and lung damage associated with smoking. What smokers really need are high-nicotine, low-tar cigarettes, so that they need to smoke less to get their nicotine and have less exposure to the more carcinogenic, destructive tars. Even better will be ways to get nicotine to the blood without smoke. Nicotine gum works well, nicotine skin patches and nasal sprays are being researched, and soon there may be capsules or tablets to satisfy the craving. They will still be hazardous to our health but much less so than cigarettes, and will clearly get rid of pollution and secondary smoker risks.