I really wish that there was a definitive answer to this, different research is leading down different paths and there is even the theory that different drugs have different mechanisms to producing addiction, not helpful! I haven't provided a reference here because I'm on my tablet and it's not proven research, I hope that's ok.
I have been taking meds (mainly opioids) for over 7 years and although I am physically dependent on them, once I am passed wds I don't struggle with not taking them...and I love that warm, fuzzy euphoria. I chase it sometimes and other times I just use my meds for pain. Is it the pain that stops addiction? And I have had terribly low places where life is not fulfilling and I do chase a high, but I only usually do it occasionally.
I've read some stuff suggestive of this but I'm yet to be convinced because I have done the same with smoking, I really enjoy it and can smoke for months and then just quit even though I do miss it. I also love, love ketamine but maybe no addiction stems from lack of supply.
I have met (in hospital for dependence, them, not me) others who cannot hoarde a pill and really suffer at the hands of addiction - even if they no longer achieve euphoria, they can't help but chase it. Yet I also know others like me, my mum is one and I have another friend that chips away, she ran through hundreds of pills of oxy over 48 hours but once the 'supply' was gone she didn't seek even though her father uses.
I don't know if anyone can shed light here. I wish humans were morehomogeneous, it would make understanding addiction so much easier.
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I concur with Logicandreason and Blight12 posts above but wrote the below before realising there was a third page of comments so I will still share rather than rewrite (I need to catch up on my sleep me-thinks) even though much was covered in these two posts.
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I think that education can play a huge role as well (both of the individual and those close to them so each individual can give their best to finding a solution for that individual). If you had the level of knowledge of some people (often those in lower socioeconomic areas as previously stated in the thread who suffer through personality, health, environment, lack of positive influences or misfortune (and of course continual drug misuse compounds all of these factors) than your level of addiction would likely be higher.
Once (fingers crossed) the war against drugs fiscal waste is channelled into scientific research than we can find more effective solutions for individuals as the bigger picture emerges.
It was only through the wisdom of other people/generosity of sharing their personal experiences that I was able to beat my very heavy addiction to alcohol (I was heading for death within a decade at the best case scenario I believe). I used meta-cognition (as Polarbearsarecool mentioned) which surely can be taught to some degree over time for most people and it was a change of view (albeit resulting from use of psychedelics, which won't necessarily work for others as good as a tool they have been for me) which enabled me to start making changes. I am more watchful of my other drug use know and will be looking to reduce over time as change my mind to my liking.
I have also found it beneficial to present myself with the argument that if I wait to use weed or lsd (which can be hard as I don't see many negatives from a relatively short period of use) than my tolerance will be decreased so I will enjoy it more and more importantly I reduce self-harm to hopefully live a longer life.
Good luck to you and your mother, I hope everyone on these forums can weigh in on these matters as much as they are able even if it is small non-intrusive advice (for particularly unreceptive people) or educating friends and family.
We can make a change even as we struggle with lessening resources on the planet and we can work around those who are less educated/prejudiced by old fashions (and unfortunately that is often politicians in my own country Australia and many others, Flynnal I somewhat understand your outrage).