Felicite Tomlinson, 18, collapsed from a suspected heart attack at her fourth floor studio apartment in Earl's Court, west London, back in March.
Her father Mark Tomlinson read a tribute to his daughter outside Westminster Coroner's Court following the verdict.
She was found by school friend Zainab Mohammed, with whom she had taken cocaine the night before her death, at around lunchtime.
It was a ideal storm, the OxyCodone, the alprazolam (Xanax) and cocaine.
Mohammed said that she wasn't aware of any drugs other than cocaine being done on that night.
Felicite Tomlinson had been battling drug addiction before her death.
The pop star's sibling had been taking drugs on a regular basis to cope with her mother's death in 2016 from leukemia, according to officials.
Boy band One Direction, from left to right, Louis Tomlinson, Liam Payne, Niall Horan, Zayn Malik, and Harry Styles arrive for the Australian Recording Industry Association (ARIA) awards in Sydney, Wednesday, Nov. 26, 2014.
During the inquest, Dr Paul Eulinger said in a statement: "She admitted she didn't want to give up drugs and she knew it could kill her".
After some persuasion, Felicite completed a successful stint in an Egyptian rehab facility in Autumn 2018 and tested clean on her return to the United Kingdom on November 26, but she relapsed in 2019.
Radcliffe also said that "her family clearly wanted her to engage with drug services", Sky News reported. Though they weren't in her system, she had used MDMA, acid and cannabis in the past.
"She was an individual who took drugs deliberately and has succumbed to their said effects accidentally", Radcliffe said. "There is no indication this was a deliberate attempt to end her life".
Mr Tomlinson added: "Felicite had huge hopes and aspirations for her future, a lot of which were beginning to come to fruition at her untimely passing".
Recounting Miss Mohammed's version of events, Dr Radcliffe said Miss Tomlinson was still breathing at 05:00 BST the next morning, but when her friend woke later at about midday she "couldn't hear breathing" from the bed next to her.