- In 20 minutes your blood pressure will drop back down to normal.
- In 8 hours the carbon monoxide (a toxic gas) levels in your blood stream will drop by half, and oxygen levels will return to normal.
- In 48 hours your chance of having a heart attack will have decreased. All nicotine will have left your body. Your sense of taste and smell will return to a normal level.
- In 72 hours your bronchial tubes will relax, and your energy levels will increase.
- In 2 weeks your circulation will increase, and it will continue to improve for the next 10 weeks.
- In three to nine months coughs, wheezing and breathing problems will dissipate as your lung capacity improves by 10%.
- In 1 year your risk of having a heart attack will have dropped by half.
- In 5 years your risk of having a stroke returns to that of a non-smoker.
- In 10 years your risk of lung cancer will have returned to that of a non-smoker.
- In 15 years your risk of heart attack will have returned to that of a non-smoker.
So, you have more immediate things to look forward to if you quit now besides just freaking out about not being able to smoke.
UPDATE: There is more information on the health effects of smoking cigarettes on Wikipedia and here is the list of 599 additives in cigarettes. Also note that "one significant issue is that while all these chemical compounds have been approved as additives to food, they were not tested by burning. Burning changes the properties of chemicals. More than 4000 chemical compounds are created by burning a cigarette."