Buddhablessd,
I am so sorry to hear about your friend's situation. I don't know if you are still in contact but hope she is doing better now. I know how hard that is to watch someone go through and the support in invaluable but self-preservation is important too.

I am curious about the study you mentioned seeing. Cigs are toxic and addictive, no doubt. The tobacco companies count on it. As far as its connection with the percentage of the mental health population begin singled out for users vs the general population, I don't know about this connection being made and would have to see the studies. It is addictive for all of the population no matter.

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In response to the other posts:

ANY substance, ANY!, put in the body can have harmful effects and why it is important to do your research, work closely with your physician, and monitor any changes that occur while on it.

Some substances have more addictive qualities than others changing neural pathways leaving an imprint, and a need for that substance. Nicotine is a primary example of this, it replaces the natural substances causing the brain to make less of its own. In time, leaving a deficit that only the stimulant can make up until a long period of absence can regenerate itself. AD's typically do not have this same permanent altering of the neural pathway, as the chemicals were not there to begin with, and why, though there may be an elimination/detoxifying period coming off of it, there are not the cravings for it afterward. In time, all of the pathways can be changed, even with addictions, and can be overcome to alter the the cravings and change the brain's chemistry, though not easy.

If there is a chemistry deficit to begin with such as with depression, then this is merely a need to compensate for what is already missing. This is not considered 'addiction'. AD's are not habit-forming and unless it is the wrong med for you, you are taking ag/ med advice, or illegally, but it is typically not harmful (unless it is the wrong one) until you find the right one and this takes time usually; but it is not addiction. Just because they are used regularly does make them habit-forming in this context; taking them daily is a habit that forms, but not a habit-forming need.

Definition of ADDICTION (Merriam -Webster)
1: the quality or state of being addicted <addiction to reading>
2: compulsive need for and use of a habit-forming substance (as heroin, nicotine, or alcohol) characterized by tolerance and by well-defined physiological symptoms upon withdrawal; broadly : persistent compulsive use of a substance known by the user to be harmful