"I saw my son fighting for his last breath," says Anna Nikolin-Caisley. "He went in agony."
Anna believes her youngest child, Vlad, 17, was "encouraged" to swallow poison by users of an online "pro-suicide" group which is still active in the UK, despite numerous calls to ban it.
Vlad's family have decided to reveal the harrowing details of his death, in Hampshire in May 2024, as a warning to others.
The government said platforms must remove illegal suicide and self-harm content when new rules come into effect this year as part of the Online Safety Act.
But the Samaritans charity says it does not believe the new law goes far enough.