i donāt think the church actually condemns smoking as a mortal sin, but drunkenness is a mortal sin, here is a list of the mortal sins that fall under the 5th commandment, taken from a basic, but very good Catechism -
*What are the mortal sins against the Fifth Commandment?
- Murder, the unjust killing of an innocent person.
- Abortion, deliberately causing the death of an unborn baby.
- Suicide, taking your own life.
- āMercy killingā, killing an innocent person who is dying of an incurable disease.
- Sterilization, making the sex organs unfruitful.
** 6. Getting drunk.**
- Serious anger and hatred.
- Helping another to commit a mortal sin.*
so thatās pretty straight forward,
but smoking, if anything, would also fall under the fifth commandment, but perhaps it would be more of a venial sin, since itās more of a habit or addiction and not such a conscious evil,
but then again, it could very well be a mortal sin depending on your knowledge of it, for example, here is a small list of the chemicals in cigarettesā¦
*Chemicals Found in Cigarette Smoke
Cigarette smoke contains over 4000 chemical compounds. Many are toxic, and some are known carcinogens. Second hand smoke is dangerous air to breathe.
Radioactive Cigarette Smoke
Lead-210 (Pb-210) and polonium-210 (Po-210) are poisonous, radioactive heavy metals that research has shown to be present in cigarette smoke.
Chemicals in Cigarettes: What They Are and How They Harm Us
The chemicals in cigarettes and cigarette smoke contain poisons, carcinogens and heavy, toxic metals.
Ammonia in Cigarettes
Ammonia is also used to boost the impact of nicotine in manufactured cigarettes.
Arsenic in Cigarette Smoke
Inorganic arsenic is present in mainstream tobacco smoke and presumably in sidestream smoke as well.
Benzene in Cigarette Smoke
Benzene is present in cigarette smoke and accounts for half of all human exposure to this health hazard.
Cadmium in Cigarettes
Cadmium is a toxic heavy metal that is present in low levels in food, and in high levels in cigarette smoke.
Carbon Monoxide in Cigarette Smoke
Carbon monoxide(CO) is a poisonous, colorless and odorless gas that is produced as a result of incomplete burning of carbon-containing fuels.
Formaldehyde in Cigarette Smoke
Formaldehyde is responsible for some of the nose, throat and eye irritation smokers experience when breathing in cigarette smoke.
Hydrogen Cyanide in Cigarette Smoke
One of the toxic byproducts of cigarette smoke is hydrogen cyanide. Smokers inhale it with every puff they take.
A Profile of Nicotine
Nicotine is a colorless, poisonous alkaloid, derived from the tobacco plant. Nicotine is also extremely addictive.
Pesticides in Cigarette Smoke
We certainly wouldnāt knowingly breathe pesticides into our lungs, yet that is exactly what smokers do every time they take a puff of a cigarette.
Tar in Cigarettes
Tar is the term used to describe the toxic chemicals found in cigarettes.
What are TSNAs?
Tobacco-specific N-nitrosamines (TSNAs) are known to be some of the most potent carcinogens present in smokeless tobacco, snuff and tobacco smoke. *
knowing that, and knowing the true danger you are putting yours and others lives in, it could possibly be considered a mortal sin, but i have to point out, i in no way can say what is or isnāt a mortal sin that the church has not declared,
but to find out, you can simply talk to your priest about it, because if he doesnāt know, then iām sure he would find out for you.
of course if your family member has any sense of morals or desire to please God, then you can try to get them to stop smoking by other means,
of course you shouldnāt hound them about it or persist if they donāt want to talk about it,
but if they are willing to listen, just talk to them about the harm they could be causing to themselves and to others, and that God is certainly not pleased with this habit, we are temples of the Holy Ghost, and to let such a poison enter into ourselves is a violation to that holy temple which is our body, smoking is a proven harmful thing, so itās without a doubt neglecting the health of our bodies, which of course God does not approve of, especially when itās done purely out of habit or craving for the purpose of ācalmingā yourself, a ācalmingā which you may have otherwise not needed were it not for the craving in the first place.
and then consider, why are you seeking your comfort from this clearly harmful thing? our comfort should be found in Godā¦
well, i would suggest talking to your priest and see what he has to say about it, cause iām not personally aware of any Church teaching on smoking as a sinā¦although now iām probably gunna look into it

which also makes me think of it another way to look at it, do you ever see priests smoking? i never have, priests know better then to get addicted to something, although i canāt say all priests are perfect, but certainly they know the dangers of being addicted to anything.
ok, hope this helps, tc.