Carbon monoxide is also found in cigarette smoke what is the effect of this gas?

Firstly you need to consider the alveoli in your lungs, these are tiny bags designed to take in and distribute the oxygen from the air around your body. Most gases that we breathe can easily pass in and out the alveoli with no issue. However there are certain gases that cannot.

Next understand the chemical make up of the carbon monoxide molecule, this is 'CO'.

Similarly the oxygen you take from the air is 'O2'.

Your lungs will readily accept the 'CO' gaseous molecule and treat it as oxygen into the alveoli, and it is at this point you become damaged. Due to the slightly different molecular structure of carbon monoxide, it becomes stuck in your lungs, congested if you like. Once this happens the effect is irreversible, you immediately reduce lung capacity and this is exactly why smokers become out of breath so quickly.

There are clearly many ill effects of chemicals such as nicotine and tar in cigarettes, as well as carcinogens such as benzine, (cancer causing). Many other conditions derived from smoking are related to oxygen starvation though, basically your body is being denied an essential fuel.