Q My husband and I are at a loss as to how to help our 20-year-old son. He was diagnosed with ADHD many years ago and has always been under the care of a psychiatrist and a psychologist. He still attends but never follows through on advice given.

He has been on Ritalin a few times through junior and second-level school but we stopped it as he suffered lots of negative side effects. He got through his Leaving Cert with support and got a college place that he is well suited for, but he failed his exams last year and has not re-engaged.

Since the summer things have gone from bad to worse and I have lost the beautiful boy I used to know. I think he is using cannabis and although he denies this, many of his new friends are definitely users. He lives with us but is rarely at home.

He has reversed his day; sleeping all day and either up all night when everybody else is in bed or out, often leaving the house at 12am or 1am. To compound the problem, he has a part-time job, and if he has the option of day or night shift, he always works nights. We firmly believe he does this so that the problems of the day cannot be dealt with, and he doesn't have to engage with us. I cannot remember the last time I had a conversation with him.

He was sporty at school and interested in music – and played guitar in a band – but he has dropped all these interests. He is and always was addicted to PlayStation games. He stays in friends' houses, or at his girlfriend's house as her parents are away a lot, and days could pass before we get contact from him. He always has an excuse: dead battery, and so on.

Over the summer my husband and I went on a week's holiday for a significant anniversary. It was our first trip on our own since our honeymoon. Our son promised he would look after the house and respect our wishes. However, our 18-year-old daughter told me quite recently that he had his girlfriend over for the week and his mates stayed over, openly drinking and smoking weed in the garden. She spent the week in her room as she was at school and very uncomfortable. Needless to say, his behaviour has a terrible effect on her: sadness at the loss of her brother is probably what she would say; him never being there for her. He appears to us to have pressed a self-destruct button, his ADHD is way out of control and we have no idea what to do.

We have offered to pay for counselling or coaching, or even a residential unit to treat his drug use, but he refuses all offers. At 20 we know we can’t drag him anywhere. He appears not to want to grow up and face reality.

A As a parent, I think it is very hard to witness the adult children you love making poor destructive choices while feeling powerless to do anything about it. Although young people over 18 are technically adults, some can remain very vulnerable, especially if they have special needs such as ADHD, or if they have not yet found their niche in life. They often continue to need some ongoing parental support.

Seek support for yourselves as parents

Even if your son won’t engage in getting some professional support, consider seeking this for yourself. You might find it useful to see a counsellor to gain emotional support to understand your feelings and put them in context. A good counsellor or family therapist may be able to help you explore practical strategies and steps for how you can manage the situation.

Even though he is an adult, you may be able to identify ways to influence your son positively and to help him cope better.

Be patient and hang in there

When dealing with troubled older teenagers and young adults, parents can swing between giving up altogether and trying to over-pressure their teenager, which often leads to great conflict or further withdrawal. There is a delicate balance to be struck between positively trying to stay involved, and stepping back and letting your son experience the consequences of his own decisions.

Generally, my advice to parents is to be patient and hang in there. Continue to try to reach out and positively influence your son, while making sure to hold him to account for his behaviour. Continue to look for times you can chat and stay connected with him, while also challenging him that he has to respect the rules of the house.

Seek to have a real conversation with him

Look for a time when you can have a real conversation with him about what is going on. When this opportunity arises, try to first understand his perspective (his own feelings about ADHD, how hard it might have been for him to say no to friends when you were away, his own potential worry about a lack of direction).

Also, share your own perspective in as positive a way as possible: your worries for him and your hopes for his future, as well as your need for him to respect people in the house and to behave responsibly.

Try to explore potential positive ways forward that you both could agree. Okay, he might not go to counselling, but what constructive options might he engage in? What are his hopes for himself?

Also, are there important influences in his life that could help? Has he some good friends who care for him? What about his relationship with his girlfriend? Are there parts of this that are good for him? What about his work and his potential interest in developing this?

Finally, try to take a long-term perspective. Stay open to the idea that he is still relatively young and still maturing. Focus on what you can do to help, while keeping his problems in perspective and making sure you get on with your own life.

Dr John Sharry is a social worker and founder of the Parents Plus charity. See .solutiontalk.ie for details of books and courses