A teenager has written an open letter to her "drug-taking" parents to thank them for showing her "life is unfair, people disappoint you".
Chelsea Cameron (18) also thanked them for missing her younger brother's first day at school and for not being there when she was made head girl.
In the letter posted on her blog, she said the difficulties she faced at home taught her to be ambitious, tolerant and independent.
She went on to become head girl of Menzieshill High School in Dundee and spoke in front of hundreds of people at her school prize giving at the city's Caird Hall.
She wrote: "Parents, both of you, thankyou for teaching me that taking drugs ruins lives, breaks families apart and gives no-one a quality of life worth living.
"I'll be eternally grateful for this lesson you have taught me which has a message which has stuck by me until this day and always will, I have never and will never have a desire to take harmful substances through your example.
"Thank-you for teaching me to be ambitious. Your example showed me that no ambition for education, work or any type of success is very harmful and leads to not a lot of self-worth.
"Your example showed me that life is all about choices and that I didn't need to make the same ones you did.
"Life is not sunshine and rainbows and thank-you for teaching me that life is unfair, people disappoint you and there's sometimes nothing you can do about that. A lesson well learnt from the both of you."
The teenager told the Dundee Evening Telegraph she was aware of drug-taking in her home from the age of seven or eight.
Her mother Tammy told the newspaper: "No child should have to go through what Chelsea did and live that kind of life.
"I am ashamed and upset at my behaviour and am so sorry and so proud of her."
In her letter, the teenager writes about how she hid the truth about her home life until third of fourth year of high school.
But she overcame her difficulties and did well at school, developing a love of languages and travel, and has been on a "trip of a lifetime" to Uganda.
She says she is a Mormon and "trying to live a Christ-like life in a world which has increasing chaos".
She said she sees her father often though has not seen her mother for a while, but dreams about a future involving both of them.
She wrote: "I hope one day that you'll wake up and realise there is so much more the world has to offer you guys and when that day comes, please come to find me so we can enjoy life together."
Ms Cameron said she hopes to inspire other people through her letter.
She told the Victoria Derbyshire programme on the BBC: "What I really hoped to do by sharing the letter was to allow people to know that they can choose positivity no matter the circumstances they're in and choose to have joy in their life no matter what happens.
"Society sometimes tells you what your fate is, it tells you that if your parents live a certain way or you live a certain lifestyle that it's destined that you live like that, and my hope is to show other young people that they can choose exactly how they want their life to be, they can choose joy and happiness and positivity no matter what the circumstances."
She said she has had an incredible response from people contacting her about her letter, and dozens have posted supportive messages on her Facebook page.
She told the programme she stopped living with her parents at the age of 14, and lived with various family members and friends on the recommendation of social workers as her father was not able to care for her and her brother.
