What Happens After You Quit Smoking: A Timeline

Quit Smoking
Some benefits of quit smoking such as the normalization of blood pressure and tissue oxygenation are seen almost immediately, cancer and other diseases can take years to lower.

Smoking is a harmful habit that can lead to severe health complications and death. Quitting smoking and overcoming tobacco cravings require determination, self-discipline, and support. When a person quits smoking, the cycle of addiction breaks. The body eventually begins to heal, and overall health improves.

Some benefits such as the normalization of blood pressure and tissue oxygenation are seen almost immediately, whereas the risks for cancer, heart disease, and lung disease can take years to lower. With each year of not smoking, the body and organs continue to heal, the risk of smoking-related disease decrease, and overall health improves.

What happens when a person stops smoking?

During the first hour:

In the first hour, the heart rate and blood pressure initially drop and then return to normal.

After 12 hours:

Cigarette smoking generates many toxins including carbon monoxide. Carbon monoxide is fatal in high doses because it prevents the delivery of oxygen to the blood and body tissues. After just 12 hours of cessation of cigarette smoking, the excess carbon monoxide is out of the system, and the oxygen levels increase.

After 24 hours:

After 24 hours of no smoking, the risk of heart disease and stroke begins to decrease.

Smoking increases blood pressure. After 24 hours, blood pressure begins to start normalizing. The oxygen levels continue to increase, improving physical stamina and heart function.

After 48 hours:

Smoking damages the nerve endings responsible for the senses of smell and taste. After 48 hours, the nerve endings begin to heal, the sense of smell and taste improves. 

After 72 hours:

After 72 hours, the nicotine levels decrease in the body. Drinking plenty of fluids and green tea can expedite the flushing of nicotine out of the body. Although it is healthier to not have nicotine in the body, this initial depletion can cause nicotine withdrawal symptoms such as mood changes, irritability, headache, and cravings.

The signs of nicotine withdrawal appear after three days. 

After one month:

After the first month, the lungs begin to heal, and lung function begins to improve. Coughing and breathing problems decrease, and physical endurance increases. Former smokers have increased stamina for cardiovascular exercises.

After one to three months:

For the next few months, blood circulation and oxygenation continue to improve.

After nine months:

Nine months after quitting, the lungs heal significantly, and lung function further improves. 

The frequency of lung infections decreases because the ability of the lungs to expel mucus and infections improves. 

After one year:

After a year of quitting, the risk of heart disease decreases by 50%. The heart function will continue to improve.

After five years:

Toxins from cigarettes cause narrowing of the blood vessels and formation of blood clots in the blood vessels. After five years of quitting, blood vessels begin to widen, and the formation of blood clots decreases. This lowers the risk of stroke.

After 10 years:

After 10 years, the risks of lung, pancreatic, mouth, and throat cancer and dying from them reduce by 50% compared with those in smokers. 

After 15 years:

After 15 years of quitting smoking, the risk of heart disease and pancreatic cancer drops to the same as a nonsmoker. 

After 20 years:

After 20 years of not smoking and exposure to cigarette smoke (second-hand smoking), the risk of death due to smoking-related diseases, including cancer, drops to that of a person who has never smoked.

References
https://www.webmd.com/smoking-cessation/what-happens-body-quit-smoking