A retired teacher who believes her son's death was caused by mental illness brought on by cannabis is touring schools to warn children about the drug.
Janie Hamilton lost her 36-year-old son James to testicular cancer after his drug-induced psychosis led him to refuse chemotherapy.
His death was recorded as being partly caused by schizophrenia, which his family believes was triggered by cannabis addiction.
James's personality changed dramatically after he became hooked on the drug at 14. He was sectioned aged 20.
He later admitted to his family that he knew cannabis caused his mental illness, but could not bring himself to stop smoking it, the MailOnline reported.
With Dorset Police, Mrs Hamilton is giving talks in assemblies beginning this month.
The former prep school music teacher from North Dorset, said she wanted youngsters to realise cannabis can be lethal. She said: "It's like Russian roulette and young people don't realise they are risking death by experimenting."
Mrs Hamilton, 65, said her son was a "brilliant writer", "witty", and dreamed of being a journalist.
He attended the Surrey boarding school where his father, now 69, taught maths, and the family lived on site.
But he had trouble fitting in and his parents believe he may have been bullied.
By age 14, he was spending time with boys outside the school, and it is thought one of them began supplying James with cannabis.
Mrs Hamilton said: "I am convinced James's psychosis began when he started smoking cannabis … It was affecting his brain. He was stony-faced and strange.
"We didn't know at the time he was doing drugs. We were naive, as we had never tried drugs ourselves."
The Hamiltons now know James smoked the drug most weekends and sometimes mid-week. He missed out on a string of A grades, losing his place at Durham University.
Mrs Hamilton knew something was wrong when he did not care about going through clearing, but she managed to help him on to another course at Birmingham.
She said he "could not cope" and dropped out after a term. Back at his parents' house, James became increasingly paranoid and withdrawn. It was then his parents believe he started to hear voices. He stripped his bedroom of everything but a futon.
One evening, he came home from work and spent all night turning in circles, waving his arms and saying: "I'm free, I'm free!"
A doctor came, followed by a social worker and psychiatrist, and they decided to section James. He was diagnosed with schizophrenia and was in hospital for three months.
After being discharged he stopped taking his schizophrenia drugs because of side effects. He soon relapsed and was in and out of hospitals for the next 16 years.
In 2014, he was found to have testicular cancer but refused to be treated and made doctors swear not to tell his family.
When they found out, the cancer was in its late stages. All they could do was offer him their care while he lived in Salisbury Hospice, Wiltshire.
Mrs Hamilton said: "In his last weeks, he became very ill with pneumonia. I asked what I could do for him and he simply said, 'Cuddle' … The doctor came a few days later and said, 'I'm sorry, he's dying' … I lived with him in the hospice for four weeks."
She added: "We were able to say all the precious things we wanted to say. I was able to tell him he was the best son I could ever have despite the anguish, stress and deep misery his cannabis-taking had caused … In his last two bed-ridden days, James was wheeled outside – he hated being inside – and slipped away peacefully."
James's death in July 2015 was recorded as malignant neoplasm of the testis and schizophrenia. Doctors said he would have agreed to potentially lifesaving treatment if he was of sound mind.
Mrs Hamilton added: "Anyone who doesn't believe cannabis can lead to mental health issues needs to come and watch the anguish and what it has done to families like ours … A lot of youngsters think they're indestructible. Cannabis is no safer than ecstasy."
Mrs Hamilton, who has a daughter with three children, planned her school tour after contacting job website Randstad's Returning To Work scheme, which helps people come back from long-term absence due to bereavement.
She said: "It's like I'm fighting back at what took my son … some good can come out of his suffering."