Dominic Elliott, 23, died after drinking a household drain cleaner made up of concentrated sulphuric acid at the painter's home in Bridlington, East Yorkshire, in March.
A two-day inquest has heard how Mr Elliott drank the liquid, which caused serious damage to his mouth and throat before perforating his stomach, after "partying" with his partner John Fitzherbert and taking drugs including cocaine and ecstasy as well as alcohol and cannabis.
Mr Fitzherbert, 48, was Hockney's long-term partner for 20 years and still lives at the artist's home and runs his domestic affairs.
After the verdict, Humberside Police confirmed an investigation is continuing into possible drugs offences following Mr Elliott's death.
A spokesman said a 48-year-old man and a 23-year-old man who were arrested on suspicion of drugs offences remained on bail as inquiries continued.
He said no one had been charged.
The East Yorkshire coroner, Professor Paul Marks, said there was "not a shred of evidence Mr Elliott intended to take his own life".
He also ruled there were no suspicious circumstances or any "third party" involvement in the death.
Prof Marks said he was recording a verdict of misadventure on the basis Mr Elliott took the substances he did in the expectation there was a risk involved.
The inquest at Hull Coroners Court heard how Mr Elliott died in the early hours of Sunday March 17 after Mr Fitzherbert took him to hospital in Scarborough.
The coroner was told Hockney was asleep in his room at the time.
The coroner said it was one of the "enigmas" of the case that Mr Elliott appeared not to be showing any signs of pain despite a pathologist saying the ingestion of the acid would have caused extreme agony.