James Fountain, 16, has been a patient at St Luke's Psychiatric Hospital, Middlesbrough, Cleveland, since he was taken there in a "hallucinogenic, psychotic state" after an hotel disco more than five weeks ago.
Police working on the theory that his drink may have been spiked in revenge for his known anti-drugs campaigning said yesterday that tests of samples taken from him had found no trace of ecstasy, LSD, cocaine, heroin or amphetamines.
Detective Chief Inspector Barry Peart, who is leading the inquiry, said he was "baffled" by the results, but James, of Hartlepool, Cleveland, had possibly been given "some other rogue substance" as yet unidentified.
Investigators found that a variety of drugs, as well as alcohol, were widely available at the pounds 6- a-head party attended by hundreds of independent-school pupils at Hardwick Hall Hotel, Sedgefield, Co Durham.
Detectives were told some youngsters had drunk a cocktail of left-overs from glasses and bottles left on tables which made some of them ill.
But there was no evidence that James, a pupil at Yarm School, had joined in, although he had apparently drunk three or four pints of lager.
Det Ch Insp Peart said many youngsters at the party had bought tablets. Some contained nothing more harmful than sugar, but others, of unknown origin, contained compounds such as rat poison or household scouring agents, and that was a particularly worrying feature of many drugs transactions.
He added: "James is still unwell in hospital and exactly how long he will remain there is not clear."
He said that one positive result of the inquiry was the "substantial amount of information officers had collected and collated about both the supply and the suppliers of drugs to schoolchildren. The response from the public had been "very positive," he said.
Police were now following "a number of other lines of inquiry," he added.Reuse content