My father is suffering from mental illness,he is a smoker and his health is so bad. How can I deter him from smoke?

You cant. Just like any addiction, they have to choose to stop themselves. As an ex-smoker, I stopped 13yrs ago, but because it was my choice. All the nagging, pleading,etc from family only made me go into stubborn mode and smoke more. My mother smoked like a chimney and would sit there and tell all of us children not to smoke with a cigarette in her hand, yep that was a real example. All five of her children grew up and started smoking. We all watched her have first heart attack at 39yrs, then sencond at 45yrs, then she had massive heart attack at 52yrs and died. We all stood around smoking like chimneys discussing how we needed to stop. Only one of us did, and that was myself, but it still took me to understand that my children were getting at the age that I couldn't tell them not to smoke with a cigarette in my hand, I decided to stop the cycle of repeating itself.
You can only hope he will want it for himself, but with his mental disorders he maynot. Be thankful you have stopped the cycle at least for your children.

Having 30 years of mental illness under my belt, and 20 of those I smoked, my doctor finally found a medication that had me put my cigarette down and never touch another one. I wasn't even trying to quit smoking, it was just a side effect of the drug called Remeron *sp?* I even gave the rest of my pack to another smoker and have had no desire to be around them at all. Also, my health has improved tremendously. I have used the patch, gum, and even hypnosis; all of these methods were a waste of money. I had a primary care physician prescribe me Welbuterine and that did not have any affect on my smoking at all. I did have cronic dry mouth with that though. Good luck and you may suggest your father ask for an anxiety medication to help him block the need or want for a cigarette.

You can't. The only person that can help him is himself. You can't make someone do something. Like a alcoholic... you have to wait it out till they get done doing what they are doing. When they are ready to stop they will. Till then just talk with him and that's all you can do.