"Given an offspring 16-18 years old (especially with health problems and alergies) how exactly can you protect them (and the entire family) from drugs (their friends do drugs and some are even mules)?"
You cannot protect your teen from making bad adult descisions.
It's hard, because you can see the dire consequences of your teen's actions, but there it is, your teen is almost an adult, and they have choices, ones you cannot control.
"The police are unhelpful (at least there was no help after 3 visits maybe the police is involved in smuggling and trafficking)"
Police enforce laws, they, also, cannot prevent a teen from making bad adult descisions.
"Psychiatrists and psychologists even less (5 different ones tried and failed)"
When Psychiatrists and Psycologists fail, it's time to fall back on medical doctors.
- Has your teen had multiple concusions? Brain damage can cause depression, which could affect their judgement.
https://paradigmtreatment.com/concussions-in-teens-mental-health/
- Has your teen been screened for ADHD? ADHD can affect their judgement.
"Teens with ADHD also are more likely to engage in impulsive, risky behaviors, including substance use and unsafe sexual activity."
https://www.nimh.nih.gov/health/publications/attention-deficit-hyperactivity-disorder-in-children-and-teens-what-you-need-to-know
- Was your teen exposed to drugs and/or alcohol before birth? Drug/Alcohol exposure before birth can affect how their brain grows and thus affect their judgement.
"Poor behavioural outcomes have been documented in a 14-year longitudinal study conducted by Streissguth et al (16). Significant deficits in antisocial and delinquent behaviours, as well as classroom and learning behaviours were noted among children with high levels of PAE (Prenatal Alcohol Exposure)(16)."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2529423/
" Prenatal cocaine exposure predicted later arrests and early onset of sexual behavior in controlled analyses."
https://pubmed.ncbi.nlm.nih.gov/24220515/
It's your job as the parent to pursue all possible reasons that your teen is showing a lack of good judgement.
"Trying to explain it thrice directly didn't work (and the other "parent" is too busy making money to even play their role as a parent and actually parent)"
Children internalize everything, so being rejected by one parent can have a devistating effect on a child's beliefs about themselves. This one issue alone, the rejection by one parent, could explain everything you've described. When a child is rejected by a parent, they feel worthless, and that feeling of being worthless can morph into a belief that they don't have a future, so they, themselves, don't care about what happens, because it all comes down to the fact that a parent has made it clear that they aren't worth any of their time or attention, the parent has taught their own child that they are worthless. All of your child's behaviors can be explained by the deep pain of being rejected.
" It has been well documented that adolescents run a heightened risk for developing depression and aggression when they feel rejected by their parents and that parental rejection has different effects for gender in developing depression and aggression. "
https://pubmed.ncbi.nlm.nih.gov/15583906/
"Maybe you can send them for some months to a summer school overseas (but what happens when they come back)."
"Exchange students exposed to the stress of living abroad showed a substantial decrease in vulnerability, which should decrease the risk of future neurotic disorders in this group. "
https://pubmed.ncbi.nlm.nih.gov/8317952/
More separation won't help. The separation will not address the lack of emotional connection between parent and teen. However, the emotional maturity gained by the teen while they are away may be of benfit, so maybe sending your teen away is a good plan?
"Maybe you can find a part-time job and have them work hard to distract them (but they are almost adults)."
Forced activities may delay the outcome, but will not treat the issue.
"The whole family is at risk (income, stability, emotion)."
Yes, the whole family is affected by the behavior of your teen. That's sort of the definition of a family, a group of people who are so important to each other that everything that happens to one of them happens to all of them.
The question is, does your teen feel like part of the family, or has the rejection of a parent forced your child to see themselves on the outside of the family, and their behavior is showing you how deeply hurt they are?
"Punishing them and threatening them doesn't work either (din't even attempt to because they did nothing explicitly wrong yet "just" bad "friends" and threatening them at this age prevents nothing)."
Punishment doesn't work, especially with teens.
"3 Ways Teenage Punishment Doesn’t Work the Way You Think in 2021"
https://teenbraintrust.com/3-ways-teenage-punishment-doesnt-work-the-way-you-think-in-2021/
"They will soon finish their school and that makes overseeing them even more difficult."
Your child is now a teen and can make bad adult descisions, whether they are near or far, working or have a lot of time off, being punished or being supported.
"Controlling Teens: Does It Work?"
https://understandingteenagers.com.au/controlling-teens-does-it-work/
It's never too late, but in order to turn this around, you, yourself, have to invest in your teen. You have to lay your own heart open for them, so they can see how deeply this affects you, and how deeply you care. There is no parenting program that will fix this, because it's no longer just a parenting problem, it's gone beyond that, it's now a family system issue, and you are the only one that can turn it around.
"It’s Never Too Late! Connecting and Reconnecting with your Teen"
https://www.inspiredlife.ca/2018/01/late-connecting-reconnecting-teen/
Your teen cannot fix this! It's too big, too scary, and has gone on for too long. You have to do the work to reach them, and that means no more punishments, no more arbitrary descisions about their life, no more treating them like a child, they are no longer you baby, they are one step from being an adult, and what your teen needs you to do is to rescue them.
You rescue them by opening your heart and your mind to them, showing them who you are and how you feel, because the only thing you can do now is make an emotional connection with your teen, and through that connection, help them make better choices.
You rescue them by looking into brain damage, ADHD, and the possible affects of fetal drug and/or alcohol exposure. You have to take them to the doctor and ask the doctor questions, and when the doctor asks you questions, you have to be honest with them. This is not a time to gloss over your child's medical history, which starts at conception. The doctor needs to know everything, absolutely everything.
It's not too late, but you may still fail, because it's rather late to address these kind of issues, but as the parent you have to try and you have put 100% into this, and be 100% committed.
Only you can turn this around. Your teen cannot fix this, it's up to you, and it's up to what you're willing to put on the line for your teen.
I would suggest you put everything on the line, because they'll know if you hold anything back, they'll know if you still wish to punish them into submission, and they'll know if you are just trying in a half-hearted way.
What they need to know is much you love and care for them, how deeply you are concerned about their safety and their future, and they need to know that whatever has happened up until now, you are choosing a new path, you are choosing your teen, you are there for them, and you want to work with them to make things better.
On the other hand, if you don't feel that connection to your teen, for whatever reason, it's still your job to find a place for your teen to finish growing into an adult where they do have 100% support and 100% committment to their wellbeing. When your child was born, you took on the responsibility of providing a safe and loving family for your child to grow up in, and if the family you have isn't safe and loving for your teen, you still carry the responsibility of providing a family that is safe and loving, and that may be with a grandparent, an aunt or uncle, or even an older sibling.
To succeed as a parent doesn't always mean that your child grows up with you. I present this option as a no-fault solution. No one is being blamed or shamed, I am simply pointing out that if it's not working with your teen in your family as it is right now, there may be a relative that can provide the family that your teen needs, and if so, as their parent, it's your responsibility to consider all of the options for what is truly best for your child.
I don't like the title of this article, but it's a good list of challenges that some parents face in truly embracing their children as they are.
" 8 Reasons Parents Fail to Love Their Kids"
https://www.psychologytoday.com/us/blog/the-human-experience/201510/8-reasons-parents-fail-love-their-kids