Is smoking a sin?
The simple answer is YES.
1. It is a dirtying of something that should be respected as holy.
Your body is the temple of the Holy Spirit. It was dipped in the Holy water of Baptism and anointed with the Holy Chrism, thus being filled with the Holy Spirit. It regularly recieves the Body and Blood of Christ in Holy Communion. Your body is a holy gift from God and should be treated with respect and care.
Could you imagine someone setting off a sooty smoke bomb next to the altar in Church? Covering the altar with black soot and ash? What a terrible thing to do! Yet when you smoke, that is exactly what you are doing. You are allowing harmful substances to enter that body sanctified by the Holy Spirit and coat your lungs with soot, and clog your blood vessels with plaques.
2. It is a form of Suicide.
Smoking is slow Suicide. There are a hundred different ways that smoking can kill or severly disable you, ranging from cancer to gangrene (your toes rot and fall off) to emphysaema (where you slowly suffocate to death over many weeks or months) to heart disease to strokes and paralysis. It contains many poisons that are harmful to your body.
We do not have the right to kill ourselves in this way or any other way - it is disobeying the 6th commandment, "You shall not murder". Not only do we have a responsibility to ourselves and to God, but also to those who love us. How do you think a child feels whose mother ends up spending weeks and weeks in hospital because of their smoking?
3. It can kill others
It has been proven that passive smoke (which comes out of the lit end of a cigarette) has six times the concentration of poisons as the smoke the smoker inhales from the filtered end. That passive smoke can cause disease in a non-smoker who breaths it by being near you. You could kill someone with your cigarette.
4. It is a form of addiction
As Christians, we have been freed by Christ and should not allow ourselves to become a slave to anything. A smoker who cannot stop will find herself often nervous and anxious because she can't get a cigarette in a meeting, or forced to miss out on activities where smoking is not allowed, or even unable to have Holy Communion. WHY??? Why do that to yourself? Why become a weak slave of a little stick of paper and leaves?
5. It is an irresponsible use of your money
Would you like someone to give you $3650 a year for doing nothing? That's what happens when a smoker who smokes a packet a day (about $10 a packet) saves when he stops smoking! Smoking is almost like taking your money and burning it. That is not a responsible thing to do. God gave each of us certain gifts and talents and we should use them not just selfishly, but to help others also. Imagine what that $3650 could do every year: how many hungry families could it feed? How many vaccinations could it give to save the lives of poor children. Or you could at least spend it on your family and friends rather than just burning it away for nothing. That is truly selfish.
This Q&A was found on Archangel Michael & St Bishoy Coptic Orthodox Church : http://www.stbishoy.org.au/modules/smartfaq/faq.php?faqid=64